Catalytic Asymmetric Synthesis of Chiral Oxaspirolactones and Tetrahydropyrans via Ammonium-Catalyzed Reactions of Vinyl Ketones and Nitroalcohols

Chiral oxaspirolactones and tetrahydropyrans are important motifs found in various bioactive molecules and pharmaceuticals. Herein, we report a highly enantioselective Michael addition-initiated reaction sequence between vinyl ketones and nitroalcohols, catalyzed by a novel chiral ammonium phase-transfer catalyst to afford the key cyclic hemiketals. These hemiketals serve as versatile intermediates for constructing oxaspirolactones and 2,5-disubstituted tetrahydropyrans with high enantioselectivity and excellent diastereoselectivity. This method features a broad substrate scope and provides access to various structurally diverse products.