Highly Regio- and Stereocontrolled Synthesis of Vinyl Sulfides via Transition-Metal-Catalyzed Hydrothiolation of Alkynes with Thiols

Abstract

Regio- and stereoselectivity in the hydrothiolation of alkynes with thiols in the presence of a variety of transition-metal catalysts is investigated in detail. Among the catalysts employed, RhCl(PPh3)3 exhibits excellent catalytic ability toward the anti-Markovnikov addition of thiols (ArSH) to alkynes (RC⋮CH), which affords the corresponding vinylic sulfides (trans-RCHCHSAr) regio- and stereoselectively. The reaction may proceed by the formation of hydrorhodium sulfide species (H−[Rh]−SAr) and probably via the subsequent hydrorhodation of alkynes to provide vinylrhodium intermediates (RCHCH−[Rh]−SAr). In contrast, PdCl2(PhCN)2-catalyzed hydrothiolation of aromatic alkynes (ArC⋮CH) takes place to give the corresponding Markovnikov adducts (R(ArS)CCH2) with excellent regioselectivity, probably via thiopalladation of alkynes by palladium sulfide species (ArS−[Pd]−Cl), which may be formed by ligand-exchange reaction between PdCl2(PhCN)2 and ArSH. Furthermore, in the case of alkynes bearing propargylic protons (R‘CH2C⋮CH), a sequential addition/isomerization reaction occurs to provide the internal vinylic sulfides (R‘CHC(SAr)CH3) regioselectively. From the same starting materials (alkyne and thiol), therefore, the regioselectivity of hydrothiolation can be attained simply by changing the catalysts, i.e., RhCl(PPh3)3 and PdCl2(PhCN)2.

Recent applications of gallium and gallium halides as reagents in organic synthesis

“…87,88 Usigi et al found that treatment of diphenyl disulfide and terminal alkynes with gallium chloride affords (E)-1,2-diphenylthio-1-alkenes selectively (Scheme 40). 89 Alkenes can be transformed in a similar fashion, affording the trans adduct.…”

Transition-Metal-Catalyzed Highly Regio- and Stereoselective Co-Polymerization of Dialkynylbenzene with Benzenedithiol Leading to Poly(Phenylene Vinylene Sulfide)

“…Recently, we have developed a series of highly selective transition-metal-catalyzed reactions of organosulfur compounds with acetylenes [30][31][32][33], and therefore this prompted us to examine the construction of -conjugated system.…”

“…On the other hand, changing the catalyst from palladium acetate to Wilkinson's catalyst (RhCl(PPh 3 ) 3 ) causes anti-Markovnikov addition of thiols to terminal alkynes with excellent stereoselectivity (syn-addition) (Scheme 2) [31]. The reaction may involve the oxidative addition of thiols to the catalyst generating HRh(SPh)Cl(PPh 3 ) 3 , followed by hydrorhodation of alkynes and reductive elimination of the product with recovery of the catalyst.…”

Sequential thiol‐ene/thiol‐ene and thiol‐ene/thiol‐yne reactions as a route to well‐defined mono and bis end‐functionalized poly(N‐isopropylacrylamide)

“…As with the thiol-ene reaction, the thiol-yne reaction, in general, proceeds rapidly under a variety of experimental conditions selectively yielding the mono or bisaddition products. [24][25][26][27][28][29] In the case of the double addition products formed under radical conditions, the reaction of two equivalents of thiol with a terminal alkyne is itself a two-step process, Scheme 2. The first, slower, step (1) involves the regiospecific antiMarkovnikov-like addition of a thiyl radical across the CBC bond yielding the intermediate vinylic radical as a mixture of the cis and trans diastereoiosomers.…”