Atropisomeric Properties of N‑Acyl/N‑Sulfonyl 5H‑Dibenzo[b,d]azepin-7(6H)‑ones

The stereochemistry of N-acyl/N-sulfonyl 5H-dibenzo­[b,d]­azepin-7­(6H)-ones (I, II) was examined in detail by freezing the conformation with a methyl group at the C-4 of dibenzoazepine. Because the two axes (axis 1, axis 2) move together concertedly, I and II exist only as a pair of enantiomers [(a1 R, a2 R) and (a1 S, a2 S)], which was confirmed by X-ray analysis of IIBc. It was elucidated that the amide derivatives I exist in equilibrium with the E/Z-amide (100:2–100:34), which means that the exocyclic bond (axis 3) is not in concert with the endocyclic axes (axis 1, axis 2). For the preparation of 5H-dibenzo­[b,d]­azepin-7­(6H)-one, the intramolecular Friedel–Crafts acylation of N-(1,1′)-biphenyl-2-yl-glycine derivatives was revisited. It was revealed that the electron-withdrawing property of the amino-protective group was a key to the success of seven-membered cyclization.