Synthesis of Spirocyclic Oxindole Dihydrothiophenes by DBU-Catalyzed [3+2] Annulation of Morita-Baylis-Hillman Carbonates with Isothiocyanates

A highly regioselective DBU-catalyzed [3 + 2] annulation of Morita-Baylis-Hillman carbonates with isothiocyanates was developed. This method allows rapid and efficient synthesis of spirocyclic oxindole dihydrothiophene products in moderate to high yields with excellent regioselectivities under simple conditions. A plausible reaction mechanism is also proposed.