Origins of the Reactivity in 1,3‐Dipolar Cycloadditions of Acyl Isocyanide Ylides

Abstract1,3‐Dipolar cycloadditions are the preferred method to generate five‐membered heterocyclic rings. Surprisingly, cycloadditions based on acyl‐isocyanide ylides have remained underexplored by the chemical community. Acyl‐isocyanide ylides readily react with dipolarophiles, such as substituted alkenes, to yield Δ1‐pyrroline derivatives. As an explanation for the observed reactivity of this reaction is lacking, extensive density functional theory calculations were performed to scrutinize the mechanistic features of the transformation. Herein we explain the experimental outcome of the reaction using a variety of reactivity theories and predict opposed regioselectivity for electron‐poor and electron‐rich dipolarophiles. With the insights obtained, we hope to incentivize the design of new cycloaddition reactions based on the acyl‐isocyanide ylides motif.