Group 13 Lewis acid-mediated formation of 5-oxazolone derivatives from tert-butyl isocyanoacetate

Abstract

tert-Butyl isocyanoacetate 1 reacted with B(C₆F₅)₃ to give a Lewis acid–base adduct 2. GaCl₃ and GaI₃ promoted cyclization affording the N-bound Lewis acid adducts of the cyclized product 5-oxazolone derivatives 3 and 4, resulting from isocyano insertion into the ester C–O bond, with the loss of isobutylene. In contrast, the reactions with InBr₃ and InI₃ afforded the analogous adducts of 5(4H)-oxazolone derivatives 5 and 6, without the loss of the tert-butyl group. A proposed reaction mechanism is provided for these reactions of 1.