Bifunctional Phosphonium Salt-catalyzed Enantioselective [4+2] Annulation of Isoindigos with Allenes: Access to Complex Heterocycles with Centerpiece of 4H-Pyrans

Structurally fused heterocycles encompassing 4H-pyran centerpiece are prevalent scaffolds with promising biological activities, but have daunting synthetic challenges. Herein, we presented a regio- and stereoselective [4+2] annulation of isoindigo derivatives with allenes by bifunctional phosphonium catalysis. This protocol provides a complementary way for accessing complex heterocyclic compounds.