Pd-Catalyzed Carbothiolation Using Thioesters with Forming a Quaternary Carbon

The Pd-catalyzed carbothiolation using thioesters with forming a quaternary carbon is described. The carbothiolation using thioesters was problematic due to a direct coupling side reaction that produced a sulfide, but this side reaction was successfully suppressed by selecting the thioester and reaction conditions. When chroman and coumaran derivatives were obtained in this reaction, the reactions with S-phenyl 4-methoxybenzothioate, Pd(PPh3)4, and Cs2CO3 at 100 °C in toluene afforded the desired products in good yields (77-92%). The carbothiolation reaction also proceeded using the ester of alkane thiol with higher yields (56-93%) when compared with the previously reported carbothiolation using TIPS thioethers (12-63%). The developed Pd-catalyzed carbothiolation is applicable for the preparation of a wide range of products including a tetralin derivative and an indoline derivative, too. The Pd-catalyzed carbothiolation using thioesters was found to be comparable to previously reported carbothiolation using TIPS thioethers in terms of yield and substrate scope, and to be a superior alternative owing to the stability and lower cost of thioesters.