Diastereoselective cycloaddition of chiral 1-acryloyl-2-imidazolidinone and o-quinodimethane generated by reduction of 1,2-bis(bromomethyl)benzene with zinc

The reduction of 1,2-bis(bromomethyl)benzene with zinc powder followed by cycloaddition with the chiral dienophile (4R,5S)-1-acryloyl-3,4-dimethyl-5-phenyl-2-imidazolidinone in the presence of BF3·Et2O under ultrasound irradiation gave the corresponding Diels–Alder cycloadduct in high yield (90%) and high diastereoselectivity (R:S = 87:13).

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(4S,5R)-1,5-Dimethyl-4-phenyl-3-((R)-1,2,3,4-tetrahydronaphthalene-2-carbonyl)imidazolidin-2-oneC22H24N2O3Ee >99%[α]D20=-41.2 (c 1.05, CHCl3)Source of chirality: (1S,2R)-(+)-norephedrineAbsolute configuration: (4S,5R,2′R)