Stoichiometry Dependence in the Consecutive, Competing Reduction, Halogenation, or Deoxygenation of Aryl Carbonyls.

Abstract

Six fundamental chemical transformations of aryl carbonyls are achieved by properly adjusting the stoichiometry of the borane-amine and titanium tetrachloride reagent system. This set of reagents acts collectively as a hydride donor, Lewis acid catalyst, and halogen source for the reduction of carbonyls to alcohols, reductive halogenation of carbonyls to halides, deoxygenation of carbonyls to alkanes, dehydroxyhalogenation of alcohols to halides, deoxygenation of alcohols to alkanes, and hydrodehalogenation of halides to alkanes. While the carbonyl reduction is broadly applicable to both aromatic and aliphatic substrates, the remaining reactions are dependent on the stability of the proposed carbocationic intermediates, enabling highly selective reactions at the substrates' benzylic position. This unique selectivity allows benzylic dehalogenation in the presence of aryl and alkyl halides in addition to highly selective dehydroxyhalogenation of alcohols even for tertiary versus secondary aliphatic and secondary versus primary benzylic substrates using only titanium tetrachloride as the chlorinating agent.