Enantioselective type II intramolecular [5 + 2] cycloadditions of oxidopyrylium ylides using chiral-phosphoric-acid catalysis

Intramolecular [5 + 2] cycloaddition reactions of oxidopyrylium ylides provide rapid access to privileged bridged seven-membered polycyclic structures. In particular, type II variants provide convenient access to highly strained adducts bearing an anti-Bredt double bond. However, enantioselective variants using catalytic methods remain unknown. Here we report an enantioselective method enabled by a non-covalent activation strategy using chiral acid catalysis. The use of a suitable leaving group in the oxidopyrylium precursor and an effective chiral-phosphoric-acid catalyst are crucial to the process. Multiple stereogenic centres can be constructed in one step with high efficiency and excellent enantioselectivity and diastereoselectivity under mild conditions. The products generated from this process are not only structurally intriguing but also represent core structures or advanced intermediates found in natural products. Both mechanistic experiments and computational calculations reveal that enolization is the rate-determining step, whereas the cycloaddition is the enantiodetermining step. Intramolecular [5 + 2] cycloaddition reactions of oxidopyrylium ylides provide access to privileged bridged seven-membered polycyclic structures. Now, an enantioselective method enabled by a non-covalent activation strategy using chiral acid catalysis is reported, allowing multiple stereogenic centres to be constructed in one step with high efficiency, enantioselectivity and diastereoselectivity.