Journal of Organic Chemistry p. 12047 - 12057 (2015)
Update date:2022-08-03
Topics:
Zhu, Wenju
Zhao, Liang
Wang, Mei-Xiang
A new strategy to construct 2,3-dihydro-1H-azepine and 1H-azepin-2(3H)-one heterocyclic rings is reported based on emerging tertiary enamide synthons. Under very mild conditions employing BBr3 as a Lewis acid catalyst and P2O5 as an additive, tertiary enamides that contain a formyl group underwent highly efficient and scalable intramolecular cyclic condensation to afford diverse 2,3-dihydro-1H-azepine and 1H-azepin-2(3H)-one derivatives in 71-96% yields. The reaction proceeded most probably through a nucleophilic addition of enamides to aldehyde, deprotonation, and dehydration cascade. Application of the method in the synthesis of dihydro-azepino[2,1-a]isoindol-5-ones, the core structure of naturally occurring lennoxamine, was also demonstrated.
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