Protic additives in aprotic solvent: a tool to improve sodium borohydride reductions of C–C bonds

This study explores the reduction of electrophilic carbon–carbon double bonds using sodium borohydride in aqueous acetonitrile to effectively protonate reactive intermediate enolate anions, thereby mitigating unwanted polymerization processes. The reduction of strong Michael acceptors leads to the corresponding saturated (‘dihydro’) analogues. In cases of electron-poor cycloheptatrienes and proaromatic cyclopropenones the initial reduction is followed by either ring-contraction or ring-opening, respectively.