| Abstrakt: |
The photochemical reactions of different N-(2-acylphenyl)-2-bromo-2-methylpropanamides have been investigated. Irradiation of the N-unsubstituted anilides 1a–1c gave the corresponding dehydrobromination, cyclization, and bromo-migration products 2, 3, and 4, respectively (Table 4;1). Irradiation of the N-alkyl anilides 1e–1g afforded the corresponding deacylation and cyclization products 5 and 6, respectively, whereas irradiation of the N-alkyl anilides 1i–1k, carrying 2-benzoyl groups on the aromatic rings, afforded the unexpected tricyclic lactams 7 (besides 2, 5, and 6). The formation of the cyclization products 6 could be rationalized in terms of an electrocyclic ring closure of the 6π-electron-conjugated enamides 2 produced by dehydrobromination of 1, followed by thermal 1,5-acyl migration (Path B in the Scheme). The formation of the bridged lactams 7 probably follows a mechanism involving the 1,7-diradical 8 generated by ζ-H-abstraction (1,8-H transfer) by an excited acyl O-atom (Path A). |
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