Synthesis of Functionalized Furans: Three‐Component Reactions Involving Ketene Dithioacetals, Acetylenes, and Phosphines to Generate Phosphorus Ylides or <i>N</i>‐Acyliminophosphoranes

Abstract Synthesis of new polysubstituted furans incorporating reactive phosphorus ylides or N ‐acyliminophosphoranes was achieved by the heterocyclization of flexible α‐acyl ketene dithioacetals. This one‐pot tandem reaction was initiated by acyl‐directed desulfurative Sonogashira coupling, followed by 1,6‐addition of phosphine to the in situ‐generated enynone and subsequent 5‐ exo ‐ dig cyclization, as well as phosphoranation. The selectivity toward the two products, i. e. α‐phosphorus ylides vs. α‐ N ‐acyliminophosphoranes‐substituted furans, was determined by both electron‐deficient acetylenes and copper salts.