DMPU catalyzed hydrosilylation of salicylaldehyde with pinacol-derived chlorosilane.

Reduction of salicyladehyde has been widely explored with catalytic protocols such as hydrogenation reactions[1], metal acid reductions[2], electron transfer and hydride transfer reductions[3,4] to the corresponding salicyl alcohol, which provides fundamental transformations in organic synthesis[5]. Salicyl alcohol is the precursor in salicylic acid metabolism which has widespread pharmaceutical applications and also employed in the synthesis of biologicallly significant compounds. Hydrosilylation procedures that make use of suitable Lewis acid/base catalysts in the reduction of carbonyl functionalities, constitute a mild and selective substitute to the conventional methods for introducing hydroxyl moiety into a given compound[6,7]. A DMPU catalyzed reduction of salicyladehyde with novel pinacol derived chlorohydrosilane in the presence of a tertiary amine to the salicyl alcohol is presented. The method tolerates an array of substituted salicylaldehyde under mild conditions to give the corresponding salicyl alcohols in moderate to excellent yields (51-97%). The reaction is proposed to proceed via a Lewis base activation of the hydrosilylether formed and a concomittant hydride delivery at the carbonyl carbon, as supported by computational calculations.