Synthesis of 6a-hydroxypterocarpans via intramolecular benzoin condensation

A novel approach for the syntheses of 6a-hydroxypterocarpans is reported. Its practicality is demonstrated by the synthesis of (±)-glycinol. The main feature is an intramolecular benzoin condensation catalyzed by nucleophilic carbenes to initiate assembly of the benzopyran and establish the 6a-hydroxy center. In addition, a one-pot method was developed to form an epoxide that facilitates subsequent cyclization leading to the benzofuran and direct production of (±)-glycinol.