Multicomponent Synthesis of 2-Aminofurans

Significance

Reported is the multicomponent synthesis of a variety of 2-aminofurans through the reaction of dialkyl acetylenedicarboxylates, isocyanates, and 2-hydroxy-1-aryl-2-(arylamino)ethanones. This reaction was somewhat unexpected, the anticipated product being the oxazine A. The mechanism of the reaction is not known; however, similar reactions with dialkyl acetylenedicarboxylates and isocyanates suggest that intermediate B should be formed. This could be expected to abstract a proton, but in the present reaction it appears to act as a nucleophile on the ketone to undergo a [3+2] cycloaddition, despite the ready availability of both an alcoholic and an aminolic proton.