Synthesis of Tofisopam by Way of Photoinduced CO₂ Fixation

Herein reported is a unique synthetic route of Tofisopam, an anxiolytic drug containing a 2,3-benzodiazepine core structure. 3,4-Dimethoxypropylbenzene and 3,4-dimethoxybenzoic acid, which are both of plant origin, and CO₂ constitute its carbon skeleton. These three renewable substances are united by two C-C bond forming reactions, i.e., a Friedel-Crafts acylation reaction and a photoinduced carboxylation reaction to construct the major carbon framework. Finally, a methyl group is introduced by a Kumada-type cross-coupling reaction to furnish Tofisopam. Various analogs of Tofisopam are readily synthesized by introducing other substituents than a methyl group at the last C-C bond forming step.