Syntheses of three 8-methoxyisoflavans from newly developed 7-benzyloxy-3-chloro-8-methoxy-2H-chromene as the precursor

We describe the formation of a 3-chloro-2H-chromene via the cascade reaction based on Claisen rearrangement of an aryl 2,3-dichloroallyl ether and the subsequent dehydrochlorination-cyclization. A divergent synthesis of three different 3-isoflavan derivatives was realized by conducting a Suzuki cross-coupling between the cascade reaction-produced 3-chloro-2H-chromene and readily preparable aryl boronic acids. By the following heterogeneous catalytic hydrogenation, we also accomplished the divergent total synthesis of isoflavan natural products (±)-duartin, (±)-7-hydroxy-2′,3′,4′,5′,8-pentamethoxyisoflavan, and (±)-8-methoxyvestitol.