Palladium-Catalyzed Carbothiolation by Using Thioesters with Formation of a Quaternary Carbon

Abstract

A Pd-catalyzed carbothiolation using thioesters, with the formation of a quaternary carbon, is described. Carbothiolation using thioesters was problematic due to a direct-coupling side reaction that produced a sulfide, but this side reaction was successfully suppressed by an appropriate selection of the thioester and the reaction conditions. In the preparation of chroman or coumaran derivatives by this method, the reaction using S-phenyl 4-methoxybenzenecarbothioate Pd(PPh₃)₄, and Cs₂CO₃ at 100 °C in toluene afforded the desired products in good yields (77–92%). The carbothiolation reaction also proceeded with esters of alkanethiols in higher yields (56–93%) than those obtained from the previously reported carbothiolation using triisopropylsilyl (TIPS) thioethers (12–63%). The developed Pd-catalyzed carbothiolation is applicable in the preparation of a wide range of products, including a tetralin derivative and an indoline derivative. The Pd-catalyzed carbothiolation using thioesters was found to be comparable with a previously reported carbothiolation using TIPS thioethers in terms of the yield and substrate scope, and to be a superior alternative owing to the stability and lower cost of thioesters.

Key words

carbothiolation - palladium catalysts - sulfides - thioesters - quaternary carbon - cascade reaction

• References and Notes

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