1,2-Reduction of α,β-unsaturated hydrazones using dimethylamine–borane/p-toluenesulfonic acid: an easy route to allyl hydrazines

α,β-Unsaturated hydrazones can be easily converted into N-allyl hydrazines by reaction with dimethylamine–borane/p-toluenesulfonic acid under mild reaction conditions. The reduction works well for N′-allylhydrazides but N′-allyl-N,N-dimethylhydrazines are rapidly reoxidised by air and so need to be manipulated under an inert atmosphere prior to N′-acylation. Competitive conjugate reduction can also be observed and the regioselectivity of the dimethylamine–borane attack is determined by steric and/or electronic factors. The procedure is also effective for the CN reduction of unconjugated hydrazones.