Catalytic Asymmetric (ene–endo)-Carbonyl–Ene Type Cyclizations

The carbonyl–ene reaction between aldehydes and olefins constitutes a perfectly atom economic approach to homoallylic alcohols with concomitant C–C bond formation. However, the scope of catalytic asymmetric intermolecular versions is currently limited to activated substrates, while of the two intramolecular types only catalytic asymmetric (ene–exo)-carbonyl–ene type cyclizations can be considered mature. The corresponding (ene–endo)-cyclizations would arguably find equal utility in chemical synthesis but remain underdeveloped. Herein, we report an efficient regio- and enantioselective catalytic asymmetric (ene–endo)-carbonyl–ene type cyclization of unbiased alkenyl aldehydes using a strong and confined IDPi Brønsted acid catalyst. High enantioselectivities of up to 98:2 e.r. were obtained for a range of homoallylic alcohols.