Conjugate addition carbon-sulfur bond formation

The reaction of crotonaldehyde and methyl vinyl ketone with thiophenol in the presence of anhydrous hydrogen chloride effects conjugate addition of thiophenol as well as acetal formation. The resulting j3-phenylthio thioacetals are converted to 1-phenylthio-and 2-phenylthio-1,3-butadiene, respectively, upon reaction with 2 equivalents of copper(I) trifluoromethanesulfonate (Table I). The copper(I)-induced heterolysis of carbon-sulfur bonds has also been used to effect pinacol-type rearrangements of bis(phenyl-thio)methyl carbinols. Thus the addition of bis(phenyl-thio)methyllithium to ketones and aldehydes followed by copper(I)-induced rearrangement results in a one-carbon ring expansion or chain-insertion transformation which gives a-phenylthio ketones. Monothioketals of 1,4-diketones are cyclized to 2,5-disubstituted furans by the action of copper(I) trifluoromethanesulfonate. ... 

Acyclic stereocontrol remains a challenging problem in synthesis. While enan-tiomerically pure sulfoxides are valuable synthetic intermediates for enantiocon-trolled carbon-carbon bond formation by conjugate addition in cyclic cases, their usefulness for such alkylations in acyclic cases has not been firmly established. Moreover, most sulfoxide directed alkylation protocols utilize the valuable sulfur auxiliary just once, which limits the synthetic versatility of the process. Marino et al. have recently reported SN2 displacements of acyclic allylic mesyloxy vinyl sulfoxides with organocopper reagents (Scheme 10).33 In addition to the excellent observed stereoselectivities, the newly created chiral center is adjacent to a vinyl sulfoxide which should allow for subsequent chirality transfer operations. On treatment with organocopper nucleophiles, both sulfoxide diastereoisomers 40b and 43b underwent SN2 displacements with high Z selectivity to yield products 42b and 45b, respectively (Table 2). The oxidation state on the sulfur was varied... 

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