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Abstract:
A highly enantioselective Brønsted acid catalyzed intramolecular carbonyl–ene reaction of olefinic aldehydes has been developed. Using a confined imidodiphosphate catalyst, the reaction delivers diverse trans-3,4-disubstituted carbo- and heterocyclic five-membered rings in high yields and with good to excellent diastereo- and enantioselectivities. ESI-MS, NMR, and DFT mechanistic studies reveal that the reaction proceeds via a stepwise pathway involving a novel covalent intermediate.