Triphenylphosphine-Catalyzed Synthesis of Dihydropyridines and Pyrans

Significance

The triphenylphosphine-catalyzed [4+2] annulation of terminal alkynes with aza-dienes and oxo-dienes is described, generating the corresponding functionalized dihydropyridines and pyrans. In general, benzoyl-substituted alkynes reliably afford the best yields of products; however, in a number of cases methyl propiolate could also be employed as a suitable reaction partner albeit with varying degrees of success. In addition, oxo-dienes required the presence of a strong electron-withdrawing group in order for the reaction to proceed. Control experiments confirmed that no reaction occurs in the absence of tri­phenylphosphine.