Photochemical reactions of N-(2-halogenoalkanoyl) derivatives of anilines

The photochemical reactions of 2-substituted N-(2-halogenoalkanoyl) derivat ives 1 of anilines and 5 of cyclic amines are described. Under irradiation, 2-bromo-2-methylpropananilides 1a-e undergo exclusively dehydrobromination to give N-aryl-2-methylprop-2-enamides (= methacrylanilides) 3a-e (Scheme 1 and Table 1). On irradiation of N-alkyl- and N-phenyl-substituted 2-bromo -2-methylpropananilides 1f-m, cyclization products, i.e. 1,3-dihydro-2H-ind ol-2-ones (= oxindoles) 2f-m and 3,4-dihydroquinolin-2(1H)-ones (= dihydroc arbostyrils) 4f-m, are obtained, besides 3f-m. On the other hand, irradiati on of N-methyl-substituted 2-chloro-2-phenylacetanilides 1o-q and 2-chloroa cetanilide Ir gives oxindoles 2o-r as the sole product, but in low yields ( Scheme 3 and Table 2). The photocyclization of the corresponding N-phenyl d erivatives 1s-v to oxindoles 2s-v proceeds smoothly. A plausible mechanism for the formation of the photoproducts is proposed (Scheme 4). Irradiation of N-(2-halogenoalkanoyl) derivatives of cyclic amines 5a - c yields the cy clization products, i.e. five-membered lactams 6a,b, and/or dehydrohalogena tion products 7a,c and their cyclization products 8a,c, depending on the ri ng size of the amines (Scheme 5 and Table 3).