Diastereoselective Synthesis of Tetrabenzohydrofuran Spirooxindoles via Diethyl Phosphite-Mediated Coupling of Isatins with <i>o</i>-Quinone Methides

Abstract

Diethyl phosphite-initiated coupling of isatins with <i>o</i>-quinone methides (<i>o</i>-QMs) is reported. This reaction involves a cascade transformation initiated by base-promoted addition of phosphite to isatins, followed by [1,2]-phospha-Brook rearrangement. This generates α-phosphonyloxy enolates that are subsequently intercepted by <i>o</i>-QMs and finally intramolecular ring closure. This protocol was used to diastereoselectively synthesize a range of <i>trans</i>-tetrabenzohydrofuran spirooxindoles in moderate to good yields with moderate to excellent diastereoselectivities.