Free-radical rearrangement of N-chloro-amides: A synthesis of lactones

Abstract

Ultraviolet irradiation of N-chlorohexanamide with subsequent hydrolysis of the crude product affords the lactones of 4- and 5-hydroxyhexanoic acids in yields of 49% and 15% respectively. Similar results were obtained using a variety of N-chloro-amides, which were conveniently prepared in high yield by the bromine-catalysed reaction of primary amides with t-butyl hypochlorite. It is suggested that the reaction proceeds by a free-radical chain mechanism involving intramolecular hydrogen-atom transfer in amide radicals formed by dissociation of the N-Cl bond. A similar transformation of N-chloro-amides may be induced by their treatment with cuprous chloride in carbon tetrachloride.