Pyrrolidine/Azepane Ring Expansion via Intramolecular Ullmann-Type Annulation/Rearrangement Cascade: Synthesis of Highly Functionalized 1H-Benzazepines

5-Arylpyrrolidine-2-carboxylates with an ortho-halogen substituent at 5-aryl and an electron-withdrawing group at the C4 position of the pyrrolidine ring were transformed into 1H-benzo[b]azepine-2-carboxylates under Cu(I) promotion and microwave activation. Reaction promoter copper(I) thiophene-2-carboxylate has been generated in situ in the reaction's environment from Cu2O and thiophene-2-carboxylic acid. Functionalized 1H-benzo[b]azepine-2-carboxylates were obtained in racemic and optically active forms in 67-89% yields. Subsequent stereoselective 1,3-dipolar cycloaddition and an Ullmann-type annulation/rearrangement cascade (UARC) ensure a synthetic route to oligomeric optically active benzazepine species with a well-defined 3D-structure.

2-[(1RS,3RS,3aRS,6aSR)-5-Benzyl-4,6-dioxo-3-phenyloctahydropyrrolo[3,4-c]pyrrol-1-yl]acetamide

In the title compound, C₂₁H₂₁N₃O₃, the relative stereochemistry of the four stereogenic C atoms has been determined. The dihedral angle between the phenyl rings is 77.63 (7)°. In the crystal, ribbons spread along the a axis are formed by N—H⋯O hydrogen bonds. C—H⋯π inter­actions also occur.