Oxidative ring-contraction of 3H-1-benzazepines to quinoline derivatives
Pulmonary Disease, Chronic Obstructive
© 2015 Elsevier Ltd. All rights reserved.When treated with SeO2, 2,4-diphenyl-3H-1-benzazepine (1) is oxidized equally at C3 and C5, giving either products of rearrangement or fragmentation; in both cases quinoline derivatives are the primary products. When C3 is oxidized, electrocyclization followed by ring-opening with phenyl migration gives the major product phenyl(3-phenylquinolin-2-yl)methanone (6), whereas C5 oxidation produces 2,4-diphenylquinoline (2) and 1,2-bis(2,4-diphenylquinolin-3-yl)diselane (8). Oxidation of C5 in 1 also results in formation of 2-(3,5-diphenylfuran-2-yl)aniline (7). On the other hand, 3-methyl-2,4-diphenyl-3H-1-benzazepine (9) upon treatment with SeO2 gives primarily a product of oxidation of C3, 2,3-diphenylquinoline (5). Oxidation of C5 in (9) is a minor pathway, and gives both 3-methyl-2,4-diphenylquinoline (10) and (3-methyl-2-phenylquinolin-4-yl)(phenyl)methanone (11). CO was detected as a byproduct in both reactions. Although the ring-contraction reaction using SeO2 has been previously noted, no mechanistic proofs have been firmly established. In this Letter, we provide evidence for the ring-contraction of benzazepines to quinolines through a fragmentation path (loss of CO and acetic acid) or through rearrangement.
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