Synthesis of fused-ring systems and diarylmethane flavonoids via ortho-quinone methide intermediates

In this study, we investigated the ability of ortho-quinone methide (o-QM), an electron-poor diene, to undergo inverse electron-demand Diels-Alder (iEDDA) reaction with electron-rich dienophiles, resulting in fused-ring flavonoid systems. In addition, we explored the Michael-type addition using o-QM and various nucleophiles, providing access to diarylmethane products. The cycloaddition reactions proceeded in a highly regioselective way, depending on the charge distribution of the reacting partners. Overall, the electron-rich dienophiles or nucleophiles reacted with the intermediate o-QM to afford products in reduced to moderate yields. Electron-poor dienophiles or nucleophiles, on the other hand, failed to react with o-QM.