Convenient access to p-conjugated 1,3-azaphospholes from alkynes via [3+2]-cycloaddition and reductive aromatization

When incorporated into p -conjugated systems, phosphorus -based heterocycles have gained significant attention due to their unique chemical and physical properties. However, their syntheses remain challenging. Herein, we describe a novel [3+2]-cycloaddition between 1,3 -dipolar triflatophosphanes and alkynes, affording azaphospholium salts. These salts can be reduced to generate the targeted 1,3-azaphospholes and an NHC (N -heterocyclic carbene) byproduct. The reaction is high -yielding, scalable, and can tolerate a wide array of sterically and electronically diverse alkynes, leading to a library of 1,3-azaphospholes (19 examples, up to 99% yield). As a broad range of structural modifications is covered, information on structure -property relationships is extracted from joint experimental and theoretical analysis, revealing efficient strategies for further optimizations. Their high thermal stability and tunable electronic structure render them a promising platform for future applications.