Base-Promoted\nChemodivergent Construction of 2<i>H</i>‑Chromen-2-one\nand Chromeno[2,3‑<i>c</i>]pyrrole Scaffolds from <i>para</i>-Quinone Methides and\nα‑Alkylidene Succinimides

Herein, we evolve a base-promoted synthesis of 2<i>H</i>-chromen-2-one and chromeno[2,3-<i>c</i>]pyrrole\nscaffolds\nvia (4 + 2) annulation of α-alkylidene succinimides with 2-hydroxyphenyl-substituted <i>para</i>-quinone methides (<i>p</i>-QMs). Extremely\nselective and switchable cyclizations were obtained by modifying the\nbase. This metal-free protocol is highlighted by its mild reaction\nconditions and broad substrate scope, and the viability of the existing\nprotocol was additionally illustrated by gram-scale synthesis and\nfurther modification. Several control experiments were performed to\nunderstand the reaction mechanism.