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.