Progress in Phosphine-Promoted Annulations between Two Electrophiles

The development of highly efficient synthetic methods of cyclic compounds is of great significance in the syntheses of pharmaceutically active molecules, natural products and other functional organic molecules. Recently, phosphine-promoted annulations of two electrophiles, which provide highly efficient access to various carbo- and heterocycles, have attracted extensive interest from synthetic chemists due to their merits such as ready availability of starting materials, mild and metal-free conditions. Generally, this kind of annulation reaction proceeds through a key step to generate an active zwitterionic intermediate via nucleophilic addition of the phosphine to an electrophile. According to different sources of the zwitterions, this review summarizes the recent progress in phosphine-promoted annulations of electron-deficient allenes, Morita-Baylis-Hillman allylic adducts, and electron-deficient alkenes with other electrophiles.