Rh-Catalyzed [4+2] Annulation of 4-Alkynals with Isocyanates

Significance

Heterocyclic compounds have long been valuable molecules whose uses range from medicinal to materials. While many transition-metal-catalyzed [2+2+2] protocols have been developed for the synthesis of six-membered heterocycles, this represents the first [4+2] annulation of this type. The use of rhodium/phosphine complexes was shown to provide the six-membered products in good yield with only one olefin isomer obtained. The use of rac-BINAP resulted in significant production of the cyclopentenone. This led to the discovery that SegPhos gave high selectivity for the kinetic resolution of the racemic starting material.