Reduction of 2-chloro-N-phenylpropanamide and 2-methyl-N-phenylaziridine with lithium aluminium hydride

Abstract

The reduction of 2-chloro-N-phenylpropanamide with LiAlH₄ has been re-examined. In contrast to previous findings, we obtain in almost equal quantities two amines from this reaction, namely N-propylaniline and the rearranged product N-isopropylaniline. 2-Methyl-N-phenylaziridine is an intermediate in the reduction and can be isolated from reactions with less LiAlH₄. Reduction of 2-methyl-N-phenylaziridine itself proceeds non-regioselectively to provide a mixture of propyl- and isopropylanilines. Formation of the amines by reduction of the aziridine is much slower than formation by reduction of the 2-chloropropanamide, which indicates that Lewis acid catalysis (by aluminium chlorohydrides) facilitates the reduction of the aziridine. In addition, Lewis acid catalysis increases the relative yield of the propylamine product. The reduction of 2-chloro-N-phenylpropanamide furnishes 2-phenylamino-1-propanol as a by-product, rather than the previously proposed 1-phenylamino-2-propanol.