Stereoselective Synthesis of 3,4-trans-Disubstituted γ-Lactams by Cerium(IV) Ammonium Nitrate Mediated Radical Cyclization of Cinnamamides

Abstract

A facile synthesis of 3,4-trans-disubstituted γ-lactams was developed, consisting of the radical cyclization of cinnam­amides mediated by cerium(IV) ammonium nitrate. The single-electron-transfer (SET) reaction of the methoxystyrenyl moiety mediated by cerium(IV) ammonium nitrate gives rise to a cation radical, whose cyclization followed by reaction with oxygen and methanol generates 3,4-trans-disubstituted γ-lactams.

cerium(IV) ammonium nitrate - intramolecular cyclization - cinnamamides - single electron transfer - γ-lactams

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10

The difference between the coupling constants for the benzylic protons in 2a (4.2 Hz) and 2a′ (2.4 Hz) indicates that the isomeric pair 2a and 2a′ differs only in the relative stereochemistry of the methoxy group at the benzylic position.