Michael addition of thioacetic and thiobenzoic acids to activated olefins was investigated in the presence of water under catalyst-free conditions. This process, in addition to being green, has an excellent yield. With simple filtration, high-quality products were obtained on a large scale. Competitive dithiane formation and ester cleavage were not observed. Also, excellent yield was obtained using this simple process for the final step of spironolactone synthesis.
