Scholarly article on topic 'Transition Metal Catalyzed Synthesis of Aryl Sulfides'

Transition Metal Catalyzed Synthesis of Aryl Sulfides Academic research paper on "Chemical sciences"

CC BY
0
0
Share paper
Academic journal
Molecules
OECD Field of science
Keywords
{""}

Academic research paper on topic "Transition Metal Catalyzed Synthesis of Aryl Sulfides"

OPEN ACCESS

molecules

ISSN 1420-3049

www.mdpi.com/journal/molecules

Review

Transition Metal Catalyzed Synthesis of Aryl Sulfides

Chad C. Eichman and James P. Stambuli *

Department of Chemistry, The Ohio State University, 100 West 18th Avenue, Columbus, OH 43210, USA

* Author to whom correspondence should be addressed; E-Mail: stambuli@chemistry.ohio-state.edu.

Received: 17 December 2010; in revised form: 10 January 2011 /Accepted: 14 January 2011 / Published: 17 January 2011

Abstract: The presence of aryl sulfides in biologically active compounds has resulted in the development of new methods to form carbon-sulfur bonds. The synthesis of aryl sulfides via metal catalysis has significantly increased in recent years. Historically, thiolates and sulfides have been thought to plague catalyst activity in the presence of transition metals. Indeed, strong coordination of thiolates and thioethers to transition metals can often hinder catalytic activity; however, various catalysts are able to withstand catalyst deactivation and form aryl carbon-sulfur bonds in high-yielding transformations. This review discusses the metal-catalyzed arylation of thiols and the use of disulfides as metal-thiolate precursors for the formation of C-S bonds.

Keywords: C-S bond formation; biaryl sulfides; arylation of thiols

1. Introduction

Over the last thirty years, significant strides have been made in organometallic processes that form carbon-sulfur bonds. Substantial growth in the transition metal-catalyzed formation of carbonheteroatom bonds has been observed, however, the development of effective C-S bond formation reactions is underdeveloped with respect to the corresponding C-N and C-O coupling reactions. The necessity for the advancement of carbon-sulfur bond forming reactions is warranted by the prevalence of biarylsulfides in natural and unnatural products that exhibit activities against cancer, HIV, Alzheimer's disease, inflammation, and asthma [1-11]. Figure 1 represents some biologically active sulfide-containing compounds.

Figure 1. Aryl sulfide-containing pharmaceuticals.

O >-"CO2H -CO2H

Methods to synthesize aryl sulfides without the use of transition metals are generally inefficient, require impractical reaction conditions, and have limited functional group tolerance. Some of these methods include nucleophilic attack on disulfides, aromatic substitution reactions, and metal-mediated disulfide reductions. The development of practical and efficient methods to create aryl sulfides has been realized through transition metal catalysis.

Transition metal-thiolate interactions are strong and numerous stable complexes have been reported in the literature. This strong coordinating ability often leads to the belief that sulfur will hinder transition metal catalytic activity. Despite this notion, thioethers can be excellent ligands for metal-catalyzed processes and metal-thiolate complexes can undergo facile reductive elimination to form C-S bonds.

Reviews discussing metal-catalyzed carbon-heteroatom bond forming reactions have been reported, including a recent excellent review on organometallic approaches to C-S bond formation [12]. This review is meant to serve as an account to discuss the proposed mechanistic aspects that allow arylsulfide formation through transition metal catalysis. The significant advances in the field will be described and when possible, mechanistic rationale will be discussed for each C-S bond forming process presented.

2. Palladium-Catalyzed Arylation of Thiols

In 1978, Migita reported the palladium-catalyzed thiation of aryl halides using Pd[PPh3]4 as a catalyst [13,14]. The method provides biaryl sulfides in good yields, but is limited to aryl bromides and also requires high reaction temperatures and long reaction times (Equation 1). Typically, the palladium-catalyzed methods following Migita's report utilize catalysts containing bidentate phosphine ligands [15-53]. The bidentate phosphine-ligated systems are proposed to be successful because of their ability to stay coordinated to the metal upon attack of the thiolates at palladium. These reactions are thought to proceed through the standard mechanism for typical palladium-catalyzed carbonheteroatom bond formations (Scheme 1).

R— SH +

Pd[PPh3]4 (10 mol %) DMSO, 100 °C

Scheme 1. General mechanism for Pd-catalyzed arylthioether synthesis.

L — Pd'' —SR

L — Pd11 — L I

Buchwald disclosed the first practical aryl sulfide synthesis from aryl chlorides [34]. This report tested a variety of monodentate and bidentate phosphine ligands, with the bidentate DiPPF ligand providing the optimal catalyst system (Equation 2). The transformation is highly efficient and functional group tolerant. The synthesis of biarylsulfides from electron rich aryl chlorides required a weaker base ("Bu3N), higher temperatures and longer reaction times to provide high yields. It is noteworthy that all bulky monodentate phosphine ligands formed unreactive catalysts. This observation was rationalized that the highly nucleophilic thiolate anions displaced the monodentate ligands and created an inactive palladium species.

R —SH +

X = Br, Cl

Pd(OAc)2 (2 mol %) DiPPF (2.4 mol %)

NaOfBu (1.2 equiv) dioxane, 100 °C, 18 h

DiPPF =

77-99%

The most significant advance in the palladium-catalyzed C-S bond formation was discovered by Hartwig and co-workers in 2006 [54,55]. Employing the strongly coordinating bidentate Josiphos ligand in the presence of a palladium salt created a highly stable and reactive catalyst. The reaction proceeds at extremely low catalyst loadings down to parts per million in palladium and can couple aryl chlorides with thiols in excellent yields (Equation 3). Functional group tolerance is very good as the reaction is effective in the presence of unprotected phenols, carboxylic acids, anilines, and amides. The rationale for the high reactivity of the catalyst system is attributed to the strong coordination ability of the Josiphos ligand.

In our recent work, the authors' discovered that aryl sulfides were formed as a byproduct of a Fukuyama coupling reaction [52]. During the course of the Fukuyama coupling [56], palladium activation of a thioester and transmetalation with an organozinc reagent produced a zinc thiolate species as a byproduct (Scheme 2).

Pd (0.01-3 mol %)

Cl CyPF-B (0.01-3 mol %) ff^T^R P<B"2

,, , + HSR -II I CyPF-(Bu = ^^ W (3)

V^ MOfBu (1.2 equiv) Y^ ÄPCy2

R1 R1 ¿^P

R DME or PhMe, 110 °C ^

70-99%

The zinc thiolate was found to act as a less nucleophilic sulfur anion in a C-S bond forming process. More importantly, the arylation of the zinc thiolate proceeded in the presence of tri-tert-butyl phosphine as a ligand. This observation led to a series of experiments to determine the factors that allow facile C-S bond formation to occur in the presence of a monodentate phosphine. It was discovered that a sub stoichiometric amount of zinc chloride alleviates strong coordination from thiolates on palladium and prevents catalyst deactivation. This method represents a rare example of a general, palladium-catalyzed aryl sulfide synthesis using a monodentate phosphine ligand.

Scheme 2. Potential pathway for the formation of aryl sulfides in the Fukuyama reaction.

Lautens and co-workers described an intramolecular C-S bond forming process with monodentate SPhos as a ligand in the palladium mediated coupling [50]. This tandem aryl sulfide formation/Suzuki-Miyaura protocol is an excellent way to create functionalized benzothiophenes in high yields (Equation 4). Similar ligands to SPhos were shown to be unreactive in palladium-catalyzed processes, however, a fast intramolecular C-S bond forming process presumably allows the transformation to occur.

R — B(OH)2 PdCl2 (3 mol % SPhos ( 3 mol %

K3PO4/Et3N ( 3 equiv) dioxane, 110 °C

PCy2 OMe

Lin and co-workers recently reported the first Pd/C catalyzed arylation of thiols [53]. This ligand-free process is limited to the use of aryl iodides and activated aryl bromides.

Hartwig and co-workers performed the first detailed mechanistic investigation for palladiummediated C-S bond formation [18,20,23]. These initial studies used tin thiolate species to investigate the transmetalation and reductive elimination steps for the process. The reductive elimination step was examined by observing the rate of arylsulfide formation from isolated Pd(II) thiolato aryl complexes (Equation 5). This pioneering mechanistic analysis of carbon-heteroatom bond forming processes revealed a significant difference between the reductive elimination of these bonds compared to C-C and C-H bonds. It was evident that the rate acceleration of the reductive elimination of electron-rich thiolates on electron poor carbons indicates nucleophilic attack by the thiolate on the carbon during reductive elimination.

'-.p SR1

50-95 °C

RSR1 + [Pd(L)2] + [Pd(PPh3)4]

Campagne and Jutand reported mechanistic studies on the palladium-mediated C-S bond forming reaction using a cysteine-derived thiol [37]. Palladium complexes of each step in the proposed catalytic cycle were detected through NMR spectroscopy and electrochemical techniques and the relative rates of reaction were measured. Interestingly, they report that a palladium thiol complex forms before deprotonation to generate a thiolate. The thiol-bound palladium complex [PhPdI(SHRXV-dppf)] was observed by 31P-NMR spectroscopy and it rapidly forms PhPd(SR)dppf upon the addition of Et3N. This reversible metallation of the thiol is proposed to facilitate the deprotonation step and would thus be applicable when weakly acidic thiols are employed. Further, the rate of reductive elimination to form the aryl sulfide was determined to be the slow step of the process. The final proposed catalytic cycle is depicted in Scheme 3.

Scheme 3. Mechanism of the palladium-catalyzed arylation of cysteine.

1/2 Pd2(dba)3 + dppf

1/2 dba

Pd0(dba)(dppf)

PhSR k = 2.3x10-4 s-1

Pd0(dppf) RSH + NEt

P—Pd''—SR

kobs > 5x10-3 s" Ph

P—Pd'' — I I

kobs = 1.3x10-3 s-'

P—Pd''—'

K = 0.4 M-1 BocHN^C02Et

RS- + H N Et3+

More recently, Hartwig has performed intensive mechanistic studies of the Josiphos-ligated catalyst system [49]. The Josiphos ligand (CyPF-fBu) is an electon-rich alkylbisphosphine that creates a highly

reactive palladium complex for the arylation of thiols. Through the isolation and reaction of each palladium complex of the catalytic cycle, it was observed that each step (oxidative addition, transmetalation, reductive elimination) proceeds within minutes at or below ambient temperature. However, the overall catalytic reaction requires temperatures of 110 °C. Based on these results, it is clear that the resting state of the reaction lies off the catalytic cycle. The resting state of the catalytic process was probed through analysis of the rate of reaction of stable complexes that preceed the catalytic cycle. Through a series of studies from isolated palladium complexes it was determined that the resting state of the reaction depended greatly on the source of palladium. A palladium-dithiolate complex represents the resting state of reactions using Pd(OAc)2 as the source of palladium. For reactions using Pd(dba)2 as the Pd-source, (LPd)2(dba) was determined to be the resting state. Lastly, for reactions catalyzed by the complex of the initial oxidative addition of aryl halide [Pd(L)(X)(Ar)], the resting state lies at a palladium hydridothiolate complex that arises from oxidative addition of Pd(0) to the S-H thiol bond. Furthermore, these results strongly correlate to the catalytic reactions of other electron-rich bisphosphines. The catalyst system developed by Buchwald using DiPPF was demonstrated to act similarly to the CyPF-tBu-ligated catalyst. The classical approach to improving a catalyst by accelerating the slow step of the catalytic cycle would fail for these reactions. For this system, acceleration of the rate of stable Pd-complexes to enter the catalytic cycle is necessary.

Scheme 4. Mechanistic details for Josiphos-ligated Pd-catalyzed C-S bond formation.

resting state when Pd(dba)2

[(LPd)2(dba)] is the Pd-source

resting state when Pd(OAc)2 is the Pd-source

+ LPd(dba) + Base

■ LPd(dba) +HSR

resting state when LPd(SR)(H)] Pd(L)(X)(Ar) is the Pd-source

L — Pd'' —SR

L—Pd''—X

- SPCy/

4. Nickel-Catalyzed Arylation of Thiols

Shortly following Migita's report on palladium-catalyzed arylation of thiols, Cristau and co-workers reported a nickel-catalyzed process to synthesize biaryl sulfides [57]. Using a nickel(II) complex with a bidentate phosphine ligand, arylsulfide formation is possible at 0.3 mol % catalyst (Equation 6). The reaction requires high temperatures and long reaction times and the yields are good to excellent.

R—Br +

SNa (0.3 mol %)

glycol, 200 °C, 24 h

65-100%

Percec reported that aryl mesylates are feasible coupling partners for nickel catalyzed C-S bond forming reactions [58]. Using 10 mol % diphenylphospinoferrocenyl nickel(II) chloride in combination with 20 mol % dppf and 1 equiv zinc metal, sodium benzenethiolate was reacted with phenylmethane sulfonate to generate diphenylsulfide in 94% yield (Equation 7). Interestingly, other aryl mesylates also produced appreciable quantities of diphenylsulfides (Equation 8). This observation was rationalized through a mechanism suggesting that C-S bond activation occurs, followed by thiolate displacement and subsequent reductive elimination of diphenylsulfide (Scheme 5). Because of this mode of reactivity, the substrate scope for this reaction is limited.

NiCl2(dppf) (10 mol %) dppf (20 mol %)

Zn (1 equiv) DMF, 80 °C

NiCl2(dppf) (10 mol %) dppf (20 mol %)

Zn (1 equiv) DMF, 80 °C

+ PhSPh (8)

Scheme 5. Mechanism of C-S bond formation using aryl mesylates.

Ar—Ni''-SPh I

Ar—Ni"-OMs I

ArOMs ArSPh

PhS-Ni"-Ph I

ArS —Ni-Ph I

Most nickel-catalyzed protocols require high catalyst loadings and long reaction times [59-65]. Recently, it was shown that strongly coordinating NHC-ligands can allow a more efficient reaction to occur (Equation 9) [66].

R-SH +

I [(IPr)Ni(allyl)Cl] (1-5 mol %)

NaO'Bu, DMF, 100 °C, 24 h

■R |Pr

76-99%

Ni, Cl

Nickel catalysts have also been shown to insert into disulfide bonds and undergo C-S bond formation. Recently, Taniguchi has reported the arylation of disulfides in the presence of bipyridyl nickel(II) bromide (Equation 10). Various aryl iodides are transformed into their corresponding aryl sulfide using 0.5 equivalents of alkyl or aryl disulfides. The reaction is postulated to proceed through an initial zinc mediated reduction of nickel(II) to the active nickel(0) complex (Scheme 6). At this stage, oxidative insertion into the aryl iodide or the disulfide is possible. In both cases, another reduction of nickel(II) is proposed and a nickel(I) species can then undergo oxidative addition of disulfide or aryl iodide to produce a nickel(III) complex. Reductive elimination then provides the aryl sulfide.

NiBr2-bpy (1:1, 10 mol %)

a' Zn (200 mol %)

+ 1/2 (RS)2 -

DMF, 110 °C

Scheme 6. Catalytic cycle for nickel-catalyzed aryl thioether synthesis using disulfides.

Ar>"'L RS I SR

(rs)2^

Ar—Ni'L

1/2 Znl

RS—Ni'L

Arl ArSR ArSR

NiXnL (n = 1 or 2)

^Nim(I)L

RS—Ni'L

^ ZnX2

; Ni''L

RS^ '' -I 1/2 Zn(SR)2

1/2 Zn

1/2 Zn

Nickel pincer complexes have also been shown to catalyze C-S bond forming reactions using disulfides and aryl iodides Equation (11) [62].

(PCP)NiCl (0.1 mol %) r^V^R (PCP)NiCl - A

RS-SR + || | -- M J (11)

Zn, DMF, 110 °C, 4 h ^^ Ph2p Ni PPh2

49-99% Cl

4. Copper-Catalyzed Arylation of Thiols

Over the last decade, copper has emerged as a viable catalyst for the arylation of thiols.[27,67-103] Palomo and co-workers demonstrated the ability of CuBr with phosphazene base to catalyze reaction between aryl iodides and thiols to afford biaryl sulfides Equation (12) [67]. Activated aryl bromides were also effective as coupling partners. Despite the high cost of the base and high catalyst loading, the reaction is efficient and established the basis for copper-catalyzed C-S bond formation.

Ar—'

CuBr (20 mol %)

(2 equiv)

2 WN-P-

Me2^P | NMe2

NMe2 NMe2 (2 equiv)

60-100%

PhMe, reflux, 1-4 h

Buchwald reported the first practical synthesis of aryl sulfides using a copper catalyst (Equation 13) [68]. Under this protocol, 5 mol % CuI with two equivalents of ethylene glycol and K2CO3 can couple thiols with aryl iodides in good to excellent yields. The substrate scope is excellent with good functional group tolerance. Notably, the reaction proceeds in the presence of anilines and phenols. The ethylene glycol likely acts as a ligand to stabilize copper during the course of the reaction.

Cu' (5 mol %) H0CH2CH20H (2 equiv)

K2C03 (2 equiv) 'Pr0H, 80 °C, 18-22 h

Recently, a highly regioselective process for the thiation of aryl halides was reported by Ranu and co-workers (Equation 14) [104]. Under this protocol, simply employing a different base significantly changes the reactivity of the copper catalyst. This alumina-supported copper catalyst has previously been employed in amination and etherification reactions. For thiation reactions, the use of K2CO3 allows the coupling of iodoarenes with thiols to occur in the presense of aryl bromides. Switching the base to Cs2CO3 under the same conditions gives a chemoselective coupling of the aryl bromide with aryl thiols. The chemoselectivity is attributed to the ability of a stronger base (Cs2CO3) to polarize the aryl bromide bond and allow copper to undergo a more facile oxidative addition of the aryl bromide compared to the K2CO3 system. Notably, the aryl amine is also not coupled with aryl bromide under these conditions.

K2C03, Cu/Al203 DMF, 110 °C

Cs2C03, Cu/Al203 DMF, 110 °C

Disulfides and thioimides have been employed as thiolate surrogates in the copper-catalyzed thiation of arylboronic acids. This modified Chan-Evans-Lam cross-coupling reaction demonstrates the diverse utility of copper salts to construct carbon-heteroatom bonds. Guy first demonstrated the ability of arylboronic acids to react with thiols to construct the arylsulfide bond in the presence of stoichiometric copper. Based on this report, Liebeskind utilized thioimides as a copper-thiolate precursor (Equation 15).[105] A copper(I)-carboxylate complex catalyzes the cross-coupling of aryl boronic acids with thioimides to generate biaryl sulfides with moderate efficacy.

R —B(OH)2 + R1S—N

CuMeSal (20-30 mol %)

THF, 45-50 °C, 2-12 h OH O

R xRi 56-83%

MeSal =

Mechanistically, the reaction is presumed to proceed through a Cu(I)-Cu(III) catalytic cycle (Scheme 7). Initial oxidative addition of the S-N bond of the thioimide, followed by transmetalation with the boronic acid generates the arylcopper(III) thiolate complex. Reductive elimination forms the aryl C-S bond and regenerates the active Cu(I)-catalyst. Consistent with this proposal, other copper carboxylates were effective in synthesizing aryl sulfide bonds.

Scheme 7. Catalytic cycle for the coupling of thioimides with boronic acids.

R1' ^R2 -v _____ Cu'(O2CAr)

R1^ .OCOAr

Cu111 i

(HO)2B-N

R1^—N

R1^ .OCOAr

R2-B(OH)2

5. Miscellaneous Transition Metal Catalysts

5.1. The case of iron vs. copper

Bolm reported the use of catalytic iron(III) chloride in the ^-arylation of thiols (Equation 16) [106]. The reaction was only compatible with aryl iodides and aryl thiols to construct biaryl sulfides.

R-SH +

FeCl3 (10 mol %)

DMEDA, NaOfBu PhMe, 135 °C, 24 h

FeCl3/Cu2O

yield [%] (GC)

> 98% (Merck)

> 98% (Aldrich)

> 99.99% (Aldrich)

> 99.99% + 10 ppm Cu2O

> 99.99% + 100 ppm Cu2O

> 99.99% + 1000 ppm Cu2O

91 4 2 42 99 93

Shortly after this report, experiments performed in the Buchwald laboratory determined that copper, as little as 10 parts per million, was essential for catalytic activity [107]. Although the presence of copper may play a role in the iron-catalyze process, the efficacy of a C-S bond formation requiring only 10 mol % FeCl3 makes for an attractive, cost-friendly process.

5.2. Cobalt-catalyzed aryltion of thiols

Cheng and co-workers disclosed a cobalt catalyzed process for the arylation of thiols (Equation 17) [108]. This method is successful for the coupling of aryl and alkyl thiols with aryl iodides and bromides.

Co'2(dppe) (1-2 mol %) 's-r

R-SH +

rY^ Zn, pyridine, CH3CN R1/s

R 80 °C, 10 h

X = ', Br

The mechanism of the cobalt catalyzed reaction is thought to occur through a cobalt(I)-(III) catalytic cycle (Scheme 8). Zinc metal reduces the starting cobalt(II) complex to the active cobalt(I) species. The reaction is then believed to undergo thiolate attack followed by oxidative addition of the aryl iodide. Reductive elimination affords the arylsulfide to complete the catalytic cycle.

Scheme 8. Cobalt-catalyze arylation of thiols

Ar1 ' — Co'''Ln SAr

Co'2(dppe) 1/2 Zn

' — Co'Ln

N©'©

Co'Ln SAr

Conclusions

Extensive work in metal-catalyzed C-S bond forming reactions has resulted in significant advances for late-metal catalyzed processes. It is evident that the palladium-catalyzed reaction creates systems with the highest yields, lowest catalyst loadings, and highest functional group tolerance. Despite this fact, expensive chiral ligands are required for high activity. Progress has been made to eliminate the requirement of these ligands through the use of zinc chloride and through the development of "ligand-free" catalysts. Other metals are growing in synthetic utility for C-S bond forming processes, such as copper and nickel. Mechanistic investigations are becoming more common in order to fully understand these catalytic processes and to ultimately advance the development of more efficient catalysts.

References

1. Sun, Z.Y.; Botros, E.; Su, A.D.; Kim, Y.; Wang, E.J.; Baturay, N.Z.; Kwon, C.H. Sulfoxide-containing aromatic nitrogen mustards as hypoxia-directed bioreductive cytotoxins. J. Med. Chem. 2000, 43, 4160-4168.

2. Wang, Y.G.; Chackalamannil, S.; Hu, Z.Y.; Clader, J.W.; Greenlee, W.; Billard, W.; Binch, H.; Crosby, G.; Ruperto, V.; Duffy, R.A.; McQuade, R.; Lachowicz, J.E. Design and synthesis of piperidinyl piperidine analogues as potent and selective M-2 muscarinic receptor antagonists. Biorg. Med. Chem. Lett. 2000, 10, 2247-2250.

3. Nielsen, S.F.; Nielsen, E.O.; Olsen, G.M.; Liljefors, T.; Peters, D. Novel potent ligands for the central nicotinic acetylcholine receptor: Synthesis, receptor binding, and 3D-QSAR analysis. J. Med. Chem. 2000, 43, 2217-2226.

4. Liu, G.; Huth, J.R.; Olejniczak, E.T.; Mendoza, R.; DeVries, P.; Leitza, S.; Reilly, E.B.; Okasinski, G.F.; Fesik, S.W.; von Geldern, T.W. Novel p-arylthio cinnamides as antagonists of leukocyte function-associated antigen-1/intracellular adhesion molecule-1 interaction. 2. Mechanism of inhibition and structure-based improvement of pharmaceutical properties. J. Med. Chem. 2001, 44, 1202-1210.

5. Clader, J.W.; Billard, W.; Binch, H.; Chen, L.Y.; Crosby, G.; Duffy, R.A.; Ford, J.; Kozlowski, J.A.; Lachowicz, J.E.; Li, S.J.; Liu, C.; McCombie, S.W.; Vice, S.; Zhou, G.W.; Greenlee, W.J. Muscarinic M2 antagonists: anthranilamide derivatives with exceptional selectivity and in vivo activity. Biorg. Med. Chem. 2004, 12, 319-326.

6. Otzen, T.; Wempe, E.G.; Kunz, B.; Bartels, R.; Lehwark-Yvetot, G.; Hansel, W.; Schaper, K.J.; Seydel, J.K. Folate-synthesizing enzyme system as target for development of inhibitors and inhibitor combinations against Candida albicans-synthesis and biological activity of new 2,4-diaminopyrimidines and 4 '-substituted 4-aminodiphenyl sulfones. J. Med. Chem. 2004, 47, 240-253.

7. Alcaraz, M.L.; Atkinson, S.; Cornwall, P.; Foster, A.C.; Gill, D.M.; Humphries, L.A.; Keegan, P.S.; Kemp, R.; Merifield, E.; Nixon, R.A.; Noble, A.J.; O'Beirne, D.; Patel, Z.M.; Perkins, J.; Rowan, P.; Sadler, P.; Singleton, J.T.; Tornos, J.; Watts, A.J.; Woodland, I.A. Efficient syntheses of AZD4407 via thioether formation by nucleophilic attack of organometallic species on sulphur. Org. Process Res. Dev. 2005, 9, 555-569.

8. Llauger, L.; He, H.Z.; Kim, J.; Aguirre, J.; Rosen, N.; Peters, U.; Davies, P.; Chiosis, G. Evaluation of 8-arylsulfanyl, 8-arylsulfoxyl, and 8-arylsulfonyl adenine derivatives as inhibitors of the heat shock protein 90. J. Med. Chem. 2005, 48, 2892-2905.

9. Gangjee, A.; Zeng, Y.B.; Talreja, T.; McGuire, J.J.; Kisliuk, R.L.; Queener, S.F. Design and synthesis of classical and nonclassical 6-arylthio-2,4-diamino-5-ethylpyrrolo[2,3-d]pyrimidines as antifolates. J. Med. Chem. 2007, 50, 3046-3053.

10. Labelle, M.; Belley, M.; Gareau, Y.; Gauthier, J.Y.; Guay, D.; Gordon, R.; Grossman, S.G.; Jones, T.R.; Leblanc, Y.; Mcauliffe, M.; Mcfarlane, C.; Masson, P.; Metters, K.M.; Ouimet, N.; Patrick, D.H.; Piechuta, H.; Rochette, C.; Sawyer, N.; Xiang, Y.B.; Pickett, C.B.; Fordhutchinson, A.W.; Zamboni, R.J.; Young, R.N. Discovery of Mk-0476, a Potent and Orally-Active

Leukotriene D-4 Receptor Antagonist Devoid of Peroxisomal Enzyme-Induction. Biorg. Med. Chem. Lett. 1995, 5, 283-288.

11. Pasquini, S.; Mugnaini, C.; Tintori, C.; Botta, M.; Trejos, A.; Arvela, R.K.; Larhed, M.; Witvrouw, M.; Michiels, M.; Christ, F.; Debyser, Z.; Corelli, F. Investigations on the 4-quinolone-3-carboxylic acid motif. 1. Synthesis-activity relationship of a class of human immunodeficiency virus type 1 integrase inhibitors. J. Med. Chem. 2008, 51, 5125-5129.

12. Bichler, P.; Love, J.A. Organometallic Approaches to Carbon-Sulfur Bond Formation. C-X Bond Formation 2010, 31, 39-64.

13. Kosugi, M.; Shimizu, T.; Migita, T. Reactions of Aryl Halides with Thiolate Anions in Presence of Catalytic Amounts of Tetrakis(Triphenylphosphine)Palladium Preparation of Aryl Sulfides. Chem. Lett. 1978, 13-14.

14. Migita, T.; Shimizu, T.; Asami, Y.; Shiobara, J.; Kato, Y.; Kosugi, M. The Palladium Catalyzed Nucleophilic-Substitution of Aryl Halides by Thiolate Anions. Bull. Chem. Soc. Jpn. 1980, 53, 1385-1389.

15. Murahashi, S.I.; Yamamura, M.; Yanagisawa, K.; Mita, N.; Kondo, K. Stereoselective Synthesis of Alkenes and Alkenyl Sulfides from Alkenyl Halides Using Palladium and Ruthenium Catalysts. J. Org. Chem. 1979, 44, 2408-2417.

16. Kosugi, M.; Ogata, T.; Terada, M.; Sano, H.; Migita, T. Palladium-Catalyzed Reaction of Stannyl Sulfide with Aryl Bromide - Preparation of Aryl Sulfide. Bull. Chem. Soc. Jpn. 1985, 58, 3657-3658.

17. Carpita, A.; Rossi, R.; Scamuzzi, B. Palladium - Catalyzed-Reactions of Trialkylstannyl Phenyl Sulfides with Alkenyl Bromides - a New Diastereoselective Synthesis of (E)-1-Alkenyl Phenyl Sulfides. Tetrahedron Lett. 1989, 30, 2699-2702.

18. Baranano, D.; Hartwig, J.F. Carbon-Heteroatom Bond-Forming Reductive Elimination -Mechanism, Importance of Trapping Reagents, and Unusual Electronic Effects during Formation of Aryl Sulfides. J. Am. Chem. Soc. 1995, 117, 2937-2938.

19. Ciattini, P.G.; Morera, E.; Ortar, G. A New, Palladium-Catalyzed Synthesis of Aromatic Mercapturic Acid-Derivatives. Tetrahedron Lett. 1995, 36, 4133-4136.

20. Louie, J.; Hartwig, J.F. Transmetalation Involving Organotin Aryl, Thiolate, and Amide Compounds - an Unusual Type of Dissociative Ligand Substitution-Reaction. J. Am. Chem. Soc. 1995, 117, 11598-11599.

21. Ishiyama, T.; Mori, M.; Suzuki, A.; Miyaura, N. The palladium-catalyzed cross-coupling reaction of 9-organothio-9-borabicyclo[3.3.1]nonanes with organic electrophiles: Synthesis of unsymmetrical sulfides. J. Organomet. Chem. 1996, 525, 225-231.

22. Hartwig, J.F. Carbon, aiHeteroatom Bond-Forming Reductive Eliminations of Amines, Ethers, and Sulfides. Acc. Chem. Res. 1998, 31, 852-860.

23. Mann, G.; Baranano, D.; Hartwig, J.F.; Rheingold, A.L.; Guzei, I.A. Carbon-sulfur bond-forming reductive elimination involving sp-, sp(2)-, and sp(3)-hybridized carbon. Mechanism, steric effects, and electronic effects on sulfide formation. J. Am. Chem. Soc. 1998, 120, 9205-9219.

24. Zheng, N.; McWilliams, J.C.; Fleitz, F.J.; Armstrong, J.D.; Volante, R.P. Palladium-Catalyzed Synthesis of Aryl Sulfides from Aryl Triflates. J. Org. Chem. 1998, 63, 9606-9607.

25. Li, G.Y. The First Phosphine Oxide Ligand Precursors for Transition Metal Catalyzed Cross-Coupling Reactions: C-C, C-N, and C-S Bond Formation on Unactivated Aryl Chlorides. Angew. Chem. Int. Ed. 2001, 40, 1513-1516.

26. Li, G.Y.; Zheng, G.; Noonan, A.F. Highly active, air-stable versatile palladium catalysts for the C-C, C-N, and C-S bond formations via cross-coupling reactions of aryl chlorides. J. Org. Chem.

2001, 66, 8677-8681.

27. Savarin, C.; Srogl, J.; Liebeskind, L.S. Substituted alkyne synthesis under nonbasic conditions: Copper carboxylate-mediated, palladium-catalyzed thioalkyne-boronic acid cross-coupling. Org. Lett. 2001, 3, 91-93.

28. Schopfer, U.; Schlapbach, A. A general palladium-catalysed synthesis of aromatic and heteroaromatic thioethers. Tetrahedron 2001, 57, 3069-3073.

29. Cacchi, S.; Fabrizi, G.; Goggiamani, A.; Parisi, L.M. Unsymmetrical Diaryl Sulfones through Palladium-Catalyzed Coupling of Aryl Iodides and Arenesulfinates. Org. Lett. 2002, 4, 4719-4721.

30. Li, G.Y. Highly Active, Air-Stable Palladium Catalysts for the C-C and C-S Bond-Forming Reactions of Vinyl and Aryl Chlorides: Use of Commercially Available [(t-Bu)2P(OH)]2PdCl2, [(t-Bu)2P(OH)PdCl2]2, and [[(t-Bu)2PO---H---OP(t-Bu)2]PdCl]2 as Catalysts. J. Org. Chem.

2002, 67, 3643-3650.

31. Bandgar, B.P.; Bettigeri, S.V.; Phopase, J. Unsymmetrical diaryl Sulfones through palladium-catalyzed coupling of aryl boronic acids and arylsulfonyl chlorides. Org. Lett. 2004, 6, 2105-2108.

32. Itoh, T.; Mase, T. A general palladium-catalyzed coupling of aryl bromides/triflates and thiols. Org. Lett. 2004, 6, 4587-4590.

33. Lengar, A.; Kappe, C.O. Tunable carbon-carbon and carbon-sulfur cross-coupling of boronic acids with 3,4-dihydropyrimidine-2-thiones. Org. Lett. 2004, 6, 771-774.

34. Murata, M.; Buchwald, S.L. A general and efficient method for the palladium-catalyzed cross-coupling of thiols and secondary phosphines. Tetrahedron 2004, 60, 7397-7403.

35. Kreis, M.; Brase, S. A general and efficient method for the synthesis of silyl-protected arenethiols from aryl halides or triflates. Adv. Synth. Catal. 2005, 347, 313-319.

36. Mispelaere-Canivet, C.; Spindler, J.F.; Perrio, S.; Beslin, P. Pd-2(dba)(3)/Xantphos-catalyzed cross-coupling of thiols and aryl bromides/triflates. Tetrahedron 2005, 61, 5253-5259.

37. Moreau, X.; Campagne, J.M.; Meyer, G.; Jutand, A. Palladium-catalyzed C-S bond formation: Rate and mechanism of the coupling of aryl or vinyl halides with a thiol derived from a cysteine. Eur. J. Org. Chem. 2005, 3749-3760.

38. Cai, L.; Cuevas, J.; Peng, Y.Y.; Pike, V.W. Rapid palladium-catalyzed cross-coupling in the synthesis of aryl thioethers under microwave conditions. Tetrahedron Lett. 2006, 47, 4449-4452.

39. Fukuzawa, S.; Tanihara, D.; Kikuchi, S. Palladium-catalyzed coupling reaction of diaryl dichalcogenide with aryl bromide leading to the synthesis of unsymmetrical aryl chalcogenide. Synlett 2006, 2145-2147.

40. Maitro, G.; Vogel, S.; Prestat, G.; Madec, D.; Poli, G. Aryl sulfoxides via palladium-catalyzed arylation of sulfenate anions. Org. Lett. 2006, 8, 5951-5954.

41. Ranu, B.C.; Chattopadhyay, K.; Banerjee, S. Indium(l) iodide promoted cleavage of diphenyl diselenide and disulfide and subsequent palladium(0)-catalyzed condensation with vinylic bromides. A simple one-pot synthesis of vinylic selenides and sulfides. J. Org. Chem. 2006, 71, 423-425.

42. Willis, M.C.; Taylor, D.; Gillmore, A.T. Palladium-catalysed intramolecular enolate O-arylation and thio-enolate S-arylation: synthesis of benzo[b]furans and benzo[b]thiophenes. Tetrahedron 2006, 62, 11513-11520.

43. Hartwig, J.F. Electronic Effects on Reductive Elimination To Form Carbon-Carbon and CarbonHeteroatom Bonds from Palladium(II) Complexes. Inorg. Chem. 2007, 46, 1936-1947.

44. Maitro, G.; Vogel, S.; Sadaoui, M.; Prestat, G.; Madec, D.; Poli, G. Enantioselective Synthesis of Aryl Sulfoxides via Palladium-Catalyzed Arylation of Sulfenate Anions. Org. Lett. 2007, 9, 5493-5496.

45. Dahl, T.; Tornoe, C.W.; Bang-Andersen, B.; Nielsen, P.; Jorgensen, M. Palladium-catalyzed three-component approach to promazine with formation of one carbon-sulfur and two carbon-nitrogen bonds. Angew. Chem. Int. Ed. 2008, 47, 1726-1728.

46. Hartwig, J.F. Carbon-heteroatom bond formation catalysed by organometallic complexes. Nature 2008, 455, 314-322.

47. Lee, J.-Y.; Lee, P.H. Palladium-Catalyzed Carbon,àiSulfur Cross-Coupling Reactions with Indium Tri(organothiolate) and Its Application to Sequential One-Pot Processes. J. Org. Chem. 2008, 73, 7413-7416.

48. Norris, T.; Leeman, K. Development of a new variant of the migita reaction for carbon-sulfur bond formation used in the manufacture of tetrahydro-4-[3-[4-(2-methyl-1H-imidazol-1-yl)phenyl]thio]phenyl-2H-pyran-4-carboxamide. Org. Process Res. Dev. 2008, 12, 869-876.

49. Alvaro, E.; Hartwig, J.F. Resting State and Elementary Steps of the Coupling of Aryl Halides with Thiols Catalyzed by Alkylbisphosphine Complexes of Palladium. J. Am. Chem. Soc. 2009, 131, 7858-7868.

50. Bryan, C.S.; Braunger, J.A.; Lautens, M. Efficient Synthesis of Benzothiophenes by an Unusual Palladium-Catalyzed Vinylic C-S Coupling. Angew. Chem. Int. Ed. 2009, 48, 7064-7068.

51. Duan, Z.Y.; Ranjit, S.; Zhang, P.F.; Liu, X.G. Synthesis of Aryl Sulfides by Decarboxylative C-S Cross-Couplings. Chem. Eur. J. 2009, 15, 3666-3669.

52. Eichman, C.C.; Stambuli, J.P. Zinc-Mediated Palladium-Catalyzed Formation of Carbon-Sulfur Bonds. J. Org. Chem. 2009, 74, 4005-4008.

53. Jiang, Z.; She, J.; Lin, X.F. Palladium on Charcoal as a Recyclable Catalyst for C-S Cross-Coupling of Thiols with Aryl Halides under Ligand-Free Conditions. Adv. Synth. Catal. 2009, 351, 2558-2562.

54. Fernandez-Rodriguez, M.A.; Shen, Q.L.; Hartwig, J.F. Highly efficient and functional-group-tolerant catalysts for the palladium-catalyzed coupling of aryl chlorides with thiols. Chem. Eur. J. 2006, 12, 7782-7796.

55. Fernandez-Rodriguez, M.A.; Shen, Q.L.; Hartwig, J.F. A general and long-lived catalyst for the palladium-catalyzed coupling of aryl halides with thiols. J. Am. Chem. Soc. 2006, 128, 2180-2181.

56. Tokuyama, H.; Yokoshima, S.; Yamashita, T.; Fukuyama, T. A novel ketone synthesis by a palladium-catalyzed reaction of thiol esters and organozinc reagents. Tetrahedron Lett. 1998, 39, 3189-3192.

57. Cristau, H.J.; Chabaud, B.; Chene, A.; Christol, H. Synthesis of Diaryl Sulfides by Nickel(Ii)-Catalyzed Arylation of Arenethiolates. Synthesis-Stuttgart 1981, 892-894.

58. Percec, V.; Bae, J.Y.; Hill, D.H. Aryl Mesylates in Metal-Catalyzed Homo-Coupling and Cross-Coupling Reactions .4. Scope and Limitations of Aryl Mesylates in Nickel-Catalyzed Cross-Coupling Reactions. J. Org. Chem. 1995, 60, 6895-6903.

59. Takagi, K. Nucleophilic Displacement Catalyzed by Transition-Metal .7. Nickel(0)-Catalyzed Synthesis of Diaryl Sulfides from Aryl Halides and Aromatic Thiols. Chem. Lett. 1987, 2221-2224.

60. Millois, C.; Diaz, P. Solution-phase synthesis of diaryl selenides using polymer-supported borohydride. Org. Lett. 2000, 2, 1705-1708.

61. Baldovino-Pantaleon, O.; Hernandez-Ortega, S.; Morales-Morales, D. Alkyl- and arylthiolation of aryl halides catalyzed by fluorinated bis-imino-nickel NNN pincer complexes [NiCl2{C5H3N-2,6-(CHNArf)(2)}]. Adv. Synth. Catal. 2006, 348, 236-242.

62. Gomez-Benitez, V.; Baldovino-Pantaleon, O.; Herrera-Alvarez, C.; Toscano, R.A.; Morales-Morales, D. High yield thiolation of iodobenzene catalyzed by the phosphinite nickel PCP pincer complex: [NiCl{C6H3-2,6-(OPPh2)(2)}]. Tetrahedron Lett. 2006, 47, 5059-5062.

63. Yatsumonji, Y.; Okada, O.; Tsubouchi, A.; Takeda, T. Stereo-recognizing transformation of (E)-alkenyl halides into sulfides catalyzed by nickel(0) triethyl phosphite complex. Tetrahedron 2006, 62, 9981-9987.

64. Yatsumonji, Y.; Ishida, Y.; Tsubouchi, A.; Takeda, T. Nickel(0) triethyl phosphite complex-catalyzed allylic substitution with retention of regio- and stereochemistry. Org. Lett. 2007, 9, 4603-4606.

65. Jammi, S.; Barua, P.; Rout, L.; Saha, P.; Punnlyamurthy, T. Efficient ligand-free nickel-catalyzed C-S cross-coupling of thiols with aryl iodides. Tetrahedron Lett. 2008, 49, 1484-1487.

66. Zhang, Y.G.; Ngeow, K.C.; Ying, J.Y. The first n-heterocyclic carbene-based nickel catalyst for C-S coupling. Org. Lett. 2007, 9, 3495-3498.

67. Palomo, C.; Oiarbide, M.; Lopez, R.; Gomez-Bengoa, E. Phosphazene bases for the preparation of biaryl thioethers from aryl iodides and arenethiols. Tetrahedron Lett. 2000, 41, 1283-1286.

68. Kwong, F.Y.; Buchwald, S.L. A general, efficient, and inexpensive catalyst system for the coupling of aryl iodides and thiols. Org. Lett. 2002, 4, 3517-3520.

69. Wan, Z.H.; Jones, C.D.; Koenig, T.M.; Pu, Y.J.; Mitchell, D. Vinyl aryl ethers from copper-catalyzed coupling of vinyl halides and phenols. Tetrahedron Lett. 2003, 44, 8257-8259.

70. Bates, C.G.; Saejueng, P.; Doherty, M.Q.; Venkataraman, D. Copper-Catalyzed Synthesis of Vinyl Sulfides. Org. Lett. 2004, 6, 5005-5008.

71. Cristau, H.J.; Cellier, P.P.; Spindler, J.F.; Taillefer, M. Highly efficient and mild copper-catalyzed N- and C-arylations with aryl bromides and iodides. Chem. Eur. J. 2004, 10, 5607-5622.

72. Zhu, W.; Ma, D. Synthesis of Aryl Sulfones via l-Proline-Promoted CuI-Catalyzed Coupling Reaction of Aryl Halides with Sulfinic Acid Salts. J. Org. Chem. 2005, 70, 2696-2700.

73. Chen, Y.-J.; Chen, H.-H. 1,1,1-Tri s(hydroxymethyl)ethane as a New, Efficient, and Versatile Tripod Ligand for Copper-Catalyzed Cross-Coupling Reactions of Aryl Iodides with Amides, Thiols, and Phenols. Org. Lett. 2006, 8, 5609-5612.

74. Enguehard-Gueiffier, C.; Thery, I.; Gueiffier, A.; Buchwald, S.L. A general and efficient method for the copper-catalyzed cross-coupling of amides and thiophenols with 6-halogenoimidazo[1,2-alpha]pyridines. Tetrahedron 2006, 62, 6042-6049.

75. Evindar, G.; Batey, R.A. Parallel synthesis of a library of benzoxazoles and benzothiazoles using ligand-accelerated copper-catalyzed cyclizations of ortho-halobenzanilides. J. Org. Chem. 2006, 71, 1802-1808.

76. Krafft, E.A.; Pinard, E.; Thomas, A.W. An improved synthesis of Lu AA20465. Tetrahedron Lett. 2006, 47, 5355-5357.

77. Kumar, S.; Engman, L. Microwave-assisted copper-catalyzed preparation of diaryl chalcogenides. J. Org. Chem. 2006, 71, 5400-5403.

78. Sawada, N.; Itoh, T.; Yasuda, N. Efficient copper-catalyzed coupling of aryl iodides and thiobenzoic acid. Tetrahedron Lett. 2006, 47, 6595-6597.

79. Taniguchi, N. Aryl- or alkylation of diaryl disulfides using organoboronic acids and a copper catalyst. Synlett 2006, 1351-1354.

80. Zheng, Y.F.; Du, X.F.; Bao, W.L. L-proline promoted cross-coupling of vinyl bromide with thiols catalyzed by CuBr in ionic liquid. Tetrahedron Lett. 2006, 47, 1217-1220.

81. Zhu, D.; Xu, L.; Wu, F.; Wan, B.S. A mild and efficient copper-catalyzed coupling of aryl iodides and thiols using an oxime-phosphine oxide ligand. Tetrahedron Lett. 2006, 47, 5781-5784.

82. Rout, L.; Sen, T.K.; Punniyamurthy, T. Efficient CuO-nanoparticle-catalyzed C-S cross-coupling of thiols with iodobenzene. Angew. Chem. Int. Ed. 2007, 46, 5583-5586.

83. Taniguchi, N. Convenient synthesis of unsymmetrical organochalcogenides using organoboronic acids with dichalcogenides via cleavage of the S-S, Se-Se, or Te-Te bond by a copper catalyst. J. Org. Chem. 2007, 72, 1241-1245.

84. Verma, A.K.; Singh, J.; Chaudhary, R. A general and efficient CuI/BtH catalyzed coupling of aryl halides with thiols. Tetrahedron Lett. 2007, 48, 7199-7202.

85. Wang, Z.M.; Mo, H.J.; Bao, W.L. Mild, efficient and highly stereoselective synthesis of (Z)-vinyl chalcogenides from vinyl bromides catalyzed by copper(I) in ionic liquids based on amino acids. Synlett 2007, 91-94.

86. Zhang, H.; Cao, W.G.; Ma, D.W. L-proline-promoted CuI-Catalyzed C-S bond formation between aryl iodides and thiols. Synth. Commun. 2007, 37, 25-35.

87. Buranaprasertsuk, P.; Chang, J.W.W.; Chavasiri, W.; Chan, P.W.H. Copper-catalyzed Ullmann coupling under ligand- and additive-free conditions. Part 2: S-arylation of thiols with aryl iodides. Tetrahedron Lett. 2008, 49, 2023-2025.

88. Evano, G.; Blanchard, N.; Toumi, M. Copper-mediated coupling reactions and their applications in natural products and designed biomolecules synthesis. Chem. Rev. 2008, 108, 3054-3131.

89. Guo, S.R.; Yuan, Y.Q. CuI/L-proline-catalyzed synthesis of vinyl sulfides in 95% alcohol. Synth. Commun. 2008, 38, 2722-2730.

90. Jiang, B.; Tian, H.; Huang, Z.G.; Xu, M. Successive copper(I)-catalyzed cross-couplings in one pot: A novel and efficient starting point for synthesis of carbapenems. Org. Lett. 2008, 10, 2737-2740.

91. Kabir, M.H.; Van Linn, M.L.; Monte, A.; Cook, J.M. Stereo- and regiospecific Cu-catalyzed, cross-coupling reaction of vinyl iodides and thiols: A very mild and general route for the synthesis of vinyl sulfides. Org. Lett. 2008, 10, 3363-3366.

92. Sperotto, E.; van Klink, G.P.M.; de Vries, J.G.; van Koten, G. Ligand-free copper-catalyzed C-S coupling of aryl iodides and thiols. J. Org. Chem. 2008, 73, 5625-5628.

93. Xu, H.-J.; Zhao, X.-Y.; Fu, Y.; Feng, Y.-S. Ligand-Free C-S Bond Formation Catalyzed by Copper(I) Oxide. Synlett 2008, 2008, 3063, 3067.

94. Bagley, M.C.; Dix, M.C.; Fusillo, V. Rapid Ullmann-type synthesis of aryl sulfides using a copper(I) catalyst and ligand under microwave irradiation. Tetrahedron Lett. 2009, 50, 3661-3664.

95. Haldon, E.; Alvarez, E.; Nicasio, M.C.; Perez, P.J. Dinuclear Copper(I) Complexes as Precatalysts in Ullmann and Goldberg Coupling Reactions. Organometallics 2009, 28, 3815-3821.

96. Luo, P.S.; Wang, F.; Li, J.H.; Tang, R.Y.; Zhong, P. Copper-Catalyzed Selective S-Arylation of

I,2-Bis(o-amino-1H-pyrazolyl) Disulfides with Arylboronic Acids. Synthesis-Stuttgart 2009, 921-928.

97. Luo, P.S.; Yu, M.; Tang, R.Y.; Zhong, P.; Li, J.H. Solvent-free copper-catalyzed oxidative S-arylation of 1,2-diaryldisulfides with aryltrimethoxysilane. Tetrahedron Lett. 2009, 50, 1066-1070.

98. Ma, D.W.; Xie, S.W.; Xue, P.; Zhang, X.J.; Dong, J.H.; Jiang, Y.W. Efficient and Economical Access to Substituted Benzothiazoles: Copper-Catalyzed Coupling of 2-Haloanilides with Metal Sulfides and Subsequent Condensation. Angew. Chem. Int. Ed. 2009, 48, 4222-4225.

99. Murru, S.; Ghosh, H.; Sahoo, S.K.; Patel, B.K. Intra- and Intermolecular C-S Bond Formation Using a Single Catalytic System: First Direct Access to Arylthiobenzothiazoles. Org. Lett. 2009,

II, 4254-4257.

100. Prasad, D.J.C.; Naidu, A.B.; Sekar, G. An efficient intermolecular C(aryl)-S bond forming reaction catalyzed by BINAM-copper(II) complex. Tetrahedron Lett. 2009, 50, 1411-1415.

101. She, J.; Jiang, Z.; Wang, Y.G. Simple, efficient and recyclable catalytic system for performing copper-catalyzed C-S coupling of thiols with aryl iodides in PEG and PEG-H2O. Tetrahedron Lett. 2009, 50, 593-596.

102. Zhao, Q.W.; Li, L.; Fang, Y.W.; Sun, D.Q.; Li, C.Z. "Ligand-Free" CuI-Catalyzed Highly Efficient Intramolecular S-Vinylation of Thiols with Vinyl Chlorides and Bromides. J. Org. Chem. 2009, 74, 459-462.

103. Ranu, B.C.; Saha, A.; Jana, R. Microwave-Assisted Simple and Efficient Ligand Free Copper Nanoparticle Catalyzed Aryl-Sulfur Bond Formation. Adv. Synth. Catal. 2007, 349, 2690-2696.

104. Bhadra, S.; Sreedhar, B.; Ranu, B.C. Recyclable Heterogeneous Supported Copper-Catalyzed Coupling of Thiols with Aryl Halides: Base-Controlled Differential Arylthiolation of Bromoiodobenzenes. Adv. Synth. Catal. 2009, 351, 2369-2378.

105. Savarin, C.; Srogl, J.; Liebeskind, L.S. A mild, nonbasic synthesis of thioethers. The copper-catalyzed coupling of boronic acids with N-thio(alkyl, aryl, heteroaryl)imides. Org. Lett. 2002, 4, 4309-4312.

106. Correa, A.; Carril, M.; Bolm, C. Iron-catalyzed S-arylation of thiols with aryl iodides. Angew. Chem. Int. Ed. 2008, 47, 2880-2883.

107. Buchwald, S.L.; Bolm, C. On the Role of Metal Contaminants in Catalyses with FeCl3. Angew. Chem. Int. Ed. 2009, 48, 5586-5587.

108. Wong, Y.C.; Jayanth, T.T.; Cheng, C.H. Cobalt-catalyzed aryl-sulfur bond formation. Org. Lett. 2006, 8, 5613-5616.

Sample Availability: Not available.

© 2011 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/).