Reactions of 2-phenyl-4H-1,3,2-benzodioxaborin, a stable ortho-quinone methide precursor

Abstract

Thermolysis of 1-phenyl-4H-1,3,2-benzodioxaborins generated the corresponding ortho-quinone methides, which were found to undergo intermolecular cycloaddition reactions with ethyl vinyl ether, dihydropyran, β-methylstyrene, cyclohexene, and 1-ethoxy-1-z-trimethylsiloxy-1-propenes to give various substituted chromans. Intramolecular trapping of the quinone methides with an olefin led to the syntheses of several analogs of tetrahydrocannabinols. ortho-Quinone methides, generated by treatment of the 2-phenyl-4H-1,3,2-benzodioxaborins with a Lewis acid, react with various nucleophiles to give the corresponding 1,4-addition products. Thus, alkyl and aryl thiols, alcohols, amine, hydride, allyl trimethylsilane, acetophenone, and diethylmalonate as well as some aryl compounds react with the quinone methide to give various 2-substituted phenols. Intramolecular reaction of the quinone methide with an aryl group led to the preparation of some 4-phenylchromans and tetralins.