Palladium-catalyzed domino sequence of ortho-X-allenyl tethered aryl isocyanides: access to fused benzazole frameworks

Abstract

A palladium-catalyzed domino sequence has been unlocked through the advent of a hitherto unreported class of ortho-X-allenyl tethered aryl isocyanides, highly reactive scaffolds that enable streamlined access to fused polycyclic heterocycles, including 2-substituted benzoxazoles, benzothiazoles, and benzimidazoles. The transformation forges two C–X and four C–C bonds in a single sequence and proceeds with broad functional-group tolerance, delivering the products in moderate to good yields. Mechanistic studies support a domino sequence involving allene isomerization, isocyanide insertion, migratory cycloisomerization, and a final [4+2] cycloaddition reaction, as validated by control experiments. This work unveils an unprecedented reactivity mode of functionalized isocyanides and provides a concise strategy for assembling densely fused heterocyclic frameworks.