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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.

Dialkyl arylphosphonates are prepared by the palladium-catalyzed reaction of aryl bromides with dialkyl phosphite in the presence of triethylamine. The similar treatment of vinyl bromides gives dialkyl vinylphosphonates stereoselectively.