93241-96-4Relevant articles and documents
Highly regio- and stereocontrolled synthesis of vinyl sulfides via transition-metal-catalyzed hydrothiolation of alkynes with thiols
Ogawa, Akiya,Ikeda, Takuma,Kimura, Kouichi,Hirao, Toshikazu
, p. 5108 - 5114 (2007/10/03)
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.
Radical-Chain Addition of Benzenethiol to Allenes. Analysis of Steric Effects and Reversibility
Pasto, Daniel J.,Warren, Steven E.,Morrison, Marjorie A.
, p. 2837 - 2841 (2007/10/02)
The radical-chain addition of benzenethiol to the monoalkylallenes 1a-e and the 1,1-dialkylallenes 6 and 8 has been studied.Attack by the benzenethiyl radical occurs at C2 and C3 of 1b-e in a ratio of 83:17.Increased attack (25percent) at C3 occurs with tert-butylallene (1a).The 1,1-dialkylallenes undergo attack only at C2.Deuterium-labeling studies indicate that the thiyl radical addition step is not detectably reversible under the reaction conditions.The internal alkene adducts 2, 3, 9 and 10 are the kinetically favored products.Rapid and reversible addition of the thiyl radical to the adducts results in complete stereochemical equilibration during the course of the reaction.The hydrogen atom abstraction step is reversible under the reaction conditions with 1a and 8 but not with 6 or the other monoalkylallenes.Treatment of the adducts derived from 1a and 8 with a catalytic quantity of iodine results in isomerization to the more thermodynamically stable adducts 4 and 11.The kinetics and thermodynamics of these reactions are discussed, and steric strain energies for the CH3...SC6H5 and t-Bu...SC6H5 interactions have been estimated to be 0.8-0.9 and 3.9-4.0 kcal/mol, respectively.
