Thiophenol, reaction with conjugated esters

Catalysts 1 and 4 are reported to give the best results for the conjugate addition of thiophenol to 2-phenylacrylates (Scheme 6.2) [17]. The products were obtained with opposite enantioselectivity in the reaction with 1 and 4, respectively, as the catalyst. Based upon a computational analysis, it was proposed that the transition state for the reaction involves hydrogen bonding between the hydroxy group of the catalyst and the carbonyl group of the ester and asymmetric proton transfer from the thiol to enolate anion (Scheme 6.2). 

Another very common phase II reaction for phenols is conjugation with sulfate to form sulfate esters (Figure 10). Other substrates for this pathway include alcohols, primary and secondary amines, hydroxyla-mines, and sulfhydryl compounds such as thiophenols. 

Catalytic asymmetric conjugate additions of heteroatoms such as nitrogen or sulfur nucleophiles provide access to important / -substituted carbonyl deri-vates, and a number of successful strategies have been devised (38, 39, 41). Tomioka developed enantioselective additions of thiophenols to ,/i-unsatu-rated esters (Equation 42) [164]. This reaction proceeds in the presence of the presumed lithium complex 220, which was suggested as the catalytically active species. As a control experiment, the chiral amino diether itself is not a catalyst for the addition of thiophenol 219 to 218. A variety of trans enoates were shown to undergo addition to give the products with high levels of induction, as illustrated by the formation of thioether 221 (99 % yield, 97 % ee). 

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