The exploration of new synthetic methods using boron mediation

Abstract

Two types of synthetic methods using boron mediation were examined. The first used either a borane or sodium triethylborohydride adduct of quinoxaline, quinazoline, or benzimidazole in an attempt to facilitate nucleophilic addition by an alkyl- or aryllithium to the heterocycle. Of these, the most successful was the quinoxaline-sodium triethylborohydride adduct, which provided a superior method for the synthesis of 2-(alkyl or aryl)-1,2,3,4-tetrahydroquinoxalines. Oxidation to the fully aromatic quinoxaline was performed using Pd/C under high temperature. The second method examined demonstrated that a triethylborane complexed imine anion mimics imine anions in alkylation reactions, but does not provide sufficient steric control to provide significant C-acylation.