Calcium-Catalyzed Bis-hydrothiolation of Unactivated Alkynes Providing Dithioacetals

Bis-hydrothiolation of alkynes providing anti-Markovnikov dithioacetals is reported. Lewis-acidic Ca(OSO2C4F9)2 (Ca(ONf)2) was synthesized for the first time and was shown to be an excellent catalyst for the transformation. The reaction is highly selective and has a wide substrate scope. It was revealed that vinyl sulfides were intermediates for this transformation and that Ca(ONf)2 efficiently catalyzed the unprecedented reactions of unactivated vinyl sulfides with thiols to afford the dithioacetals in good to high yields.