On the Reaction of N-Bromoacetamide with Olefins. Preparation and Chemistry of 2-Bromo-N-Bromoacetimidates, a New Class of Compounds

Abstract

A historical and mechanistic review of the Wohl-Ziegler reaction (allylic bromination by N-bromo-amides and imides) is presented as an introduction to the present work, a re-examination of the reaction of N-bromoacetamide (NBA) with some olefins. The reaction has been found to lead not to allylic bromination but, rather, to 2-bromo-N-bromoacetimidates, a new class of compounds. The stoichiometry of the reaction is: olefin + 2 NBA → adduct + acetamide. The process appears to occur in two stages, viz., a free radical reaction of NBA with itself to form N,N-dibromoacetamide (NDBA), followed by ionic addition of NDBA to the double bond. Hofmann's synthesis of NDBA has been repeated; the compound reacts rapidly with cyclohexene to give the same adduct 10 as does NBA. A variety of stereochemical and selectivity data suggest that this is an ionic addition.The chemical transformations of 2-bromo-N-bromoacetimidates under thermal, acidic, and basic conditions are discussed.