Asymmetric Synthesis of cis-3,4-Disubstituted Chromans and Dihydrocoumarins via an Organocatalytic Michael Addition/Hemiacetalization Reaction

The organocatalytic domino Michael/hemiacetalization reaction between various aldehydes and ortho-nitrovinylphenols has been developed. Under the catalysis of diphenyl prolinol trimethylsilyl ether, cis-3,4-disubstituted chromanols are obtained in high to excellent yields (81-98%) and stereoselectivities (dr: 86:14 to >99:1, ee 96 to > 99%). The corresponding disubstituted chromans are available by dehydroxylation of the domino products in good to excellent yields (58-95%). Furthermore, oxidation of the domino products with pyridinium chlorochromate provided 3,4-dihydrocoumarins in good yields (65-83%) without any epimerization.