Photochemical Reactions of Enamino Ketones

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Abstract
Photochemical reactions of N-aryl enamino ketones including one enone system and one divinylamine system in the molecule were examined. Photochemical behaviours of N-aryl enamino ketones differed for the tertiary and secondary amines involved. While 5,5-dimethyl-3-(N-methylanilino)cyclohex-2-en-1-one gave an oxidative cyclization product, 3-anilino-5,5-dimethyl-cyclohex-2-en-1-one gave two major products and a minor one. One of the major products was characterized as 3,3-dimethyl-5-hydroxy-3,4-dihydro-1-benzazocines by their elemental analyses and spectroscopic properties. The compounds showed 6π system pseudo aromaticity in their NMR spectra. The temperature-dependent NMR signals for gem-dimethyl protons were due to the flapping of the 8-membered ring. The reduction product with diborane was identified as 1,2,3,4,5,6-hexahydro-1-benzazocine by comparison with an authentic sample. The other major product was a ketene adduct and the minor product, a lactone.