Selective Reductions. XVIII. The Fast Reaction of Primary, Secondary, and Tertiary Amides with Diborane. A Simple, Convenient Procedure for the Conversion of Amides to the Corresponding Amines

Abstract

.Primary, secondary, and tertiary amide derivatives of both aliphatic and aromatic carboxylic acids were reduced rapidly and quantitatively into the corresponding amines by excess diborane in refluxing tetrahydrofuran. Highly reactive tertiary amides, such as N,N-dimethylpivalamide, were reduced at moderate rates even at room temperature. The ease of reduction of the different amide functions, as revealed by the rate studies, follows the order tertiary amide ≥ secondary amide >> primary amide. Primary aliphatic amides are reduced at faster rates than primary aromatic amides. Unlike lithium aluminum hydride reductions, the tendency for C-N bond cleavage to yield alcohol is completely absent. The mildness of the reagent, diborane, permits the presence of other substituents less susceptible to the reducing action of the reagent, such as nitro, ester groups, halogen, etc. This reaction provides a convenient synthetic procedure for the selective reduction of amides where this is required in synthetic operations. © 1973, American Chemical Society. All rights reserved.