Synthesis of fused-pyran derivatives via a base-mediated annulation of bis-allenoates followed by auto-oxidation in air

Abstract

We introduce, for the first time, an inorganic base-mediated cyclization and auto-oxidation of bisallenones/bisalkynones. This reaction is realized under mild conditions through precise control of the base and atmosphere, providing a wide range of structurally diverse fused-pyran derivatives with moderate to excellent yields. Utilizing KOH as the initiator under a nitrogen atmosphere, a series of novel cyclohexane-fused pyran derivatives was obtained as the primary product. In contrast, under aerobic conditions with Na₂S as the catalyst, oxidative cyclization predominantly occurred, yielding cyclohexanone-fused pyran derivatives. The protocol also exhibits significant regioselectivity, particularly when asymmetric bisallenones/bisalkynones are selected as substrates.