An efficient organocatalytic asymmetric synthesis of 2,3,4-trisubstituted tetrahydrofurans and tetrahydropyrans has been developed using tandem iminiumÀ enamine catalysis. The process comprises of a double Michael addition reaction between γ/δ-hydroxy-α,β-unsaturated carbonyls and enals. The products of this reaction are obtained in high enantio-and diasteroselectivities and some further synthetic transformations have been performed.
A method for the organocatalytic, highly enantioselective, and moderately diastereoselective dimerization (redox isomerization/acetal formation) of γ‐hydroxyenones is disclosed. The stereogenic acetal products were obtained via hemiacetal intermediates followed by a cyclization reaction. With bifunctional thiourea catalysts, high yields and excellent enantioselectivities were achieved for a variety of acetal products under mild reaction conditions. In addition, detailed DFT calculations were performed to investigate the mechanism of this reaction, and these calculations suggested that the diastereoselectivity was due to a kinetically controlled process.
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