Selective Reduction of Carboxylic Acid Derivatives by Catalytic Hydrosilylation

In the last decade, an increasing number of useful catalytic reductions of carboxylic acid derivatives with hydrosilanes have been developed. Notably, the combination of an appropriate silane and catalyst enables unprecedented chemoselectivity that is not possible with traditional organometallic hydrides or hydrogenation catalysts. For example, amides and esters can be reduced preferentially in the presence of ketones or even aldehydes. We believe that catalytic hydrosilylations will be used more often in the future in challenging organic syntheses, as the reaction procedures are straightforward, and the reactivity of the silane can be fine-tuned. So far, the synthetic potential of these processes has clearly been underestimated. They even hold promise for industrial applications, as inexpensive and readily available silanes, such as polymethylhydrosiloxane, offer useful possibilities on a larger scale. Time for a change: Excellent chemoselectivity that is not attainable with traditional organometallic hydrides and hydrogenation catalysts is often observed in the catalytic hydrosilylation of carboxylic acid derivatives (see scheme). Moreover, hydrosilanes are easy-to-use reducing agents that can be activated under mild conditions. Until now, the potential of such reactions, which could be useful in complex organic synthesis, has been underestimated. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.