8.03 Reduction of C[dbnd]N to CHNH by Hydride Delivery from C

Abstract

The reduction of imines by hydride delivery from C provides alternatives to traditional methods in which H2 and metal hydrides are used as reductants for the synthesis of amines. Since the 1990s highly enantioselective reductions have been achieved founded on new catalytic strategies. Starting with a brief description of the difficulties arising from imine substrates and the different hydride sources and strategies to manage this transformation, this chapter examines transfer hydrogenation using formic acid, 2-propanol, Hantzsch esters, and other N-heterocycles, as well as the indirect reductive methods in which silanes are used as alternative organic reductants. Novel organocatalytic approaches have played an important role and are highlighted in the text. An overview of the scope, conditions, effectiveness, and selectivity of the reaction is provided, evaluating the advantages and weaknesses of the different strategies. Finally, recent progress in the synthesis of amines through reductive amination is discussed.