Alkaline Earth Catalyzed CO2 Hydroboration into Acetal Derivatives Leading to C–S Bond Formation

The use of Mg and Ca hydride catalysts for the 4e– reduction of CO2 is reported. Borabicyclo[3.3.1]nonane (9-BBN) and dicyclohexylborane (HBCy2), as reductants, led to the generation of the corresponding bis(boryl)acetal (BBA) which in situ reacted with thiol to afford new borylated hemithioacetal compounds (R2BOCH2SR) under mild neutral conditions. These hemithioacetals were then converted into dithioacetal (RSCH2SR) with the addition of a second equivalent of thiol under acidic activation, or amino-methyl sulfide (RSCH2NR2) upon reaction with secondary amine.