Beyond the Five and Six: Evaluation of Seven-Membered Cyclic Anhydrides in the Castagnoli–Cushman Reaction

The Castagnoli–Cushman reaction with benzo­[d]­oxepine-2,4­(1H,5H)-dione as an anhydride component allowed for preparation of 2,3-disubstituted 4-oxo-2,3,4,5-tetrahydro-1H-benzo­[d]­azepine-1-carboxylic acids in 21–75% yields and with good trans diastereoselectivity. The method worked with imines generated from aromatic or α-branched aliphatic aldehydes and is amenable for both parallel synthesis and scale-up. The procedure for epimerization of the resulting trans-disubstituted tetrahydrobenzo­[d]­azepines to their cis isomers was also developed.