Phosphine-containing Lewis base catalyzed cyclization of benzofuranone type electron-deficient alkenes with allenoates: a facile synthesis of spirocyclic benzofuranones
A highly enantioselective [4 + 2] cycloaddition of allenoates with 2-olefinic benzofuran-3-ones catalyzed by (DHQD)2AQN, which allowed the synthesis of optically active dihydropyran-fused benzofurans, was developed.