Synthesis of indolones via radical cyclization of N-(2-halogenoalkanoyl)substituted anilines

The radical reactions of N-(2-halogenoalkanoyl)-substituted anilines (anilides) of type 1 have been investigated under various conditions. Treatment of compounds 1a-1o with Bu3SnH in the presence of (2,2'-azobis(isobutyronitrile) (AIBN) afforded a mixture of the indolones (oxindoles) 2a-2o and the reduction products 5a-5o (Table 1). In contrast, the N-unsubstituted anilides 1p-1s, 1u, and 1v gave the corresponding reduction products exclusively (Table 1). Similar results were obtained by treatment of 1 with Ni powder (Table 2) or wth Et3B (Table 3). Anilides with longer N-(phenylalkyl) chains such as 6 and 7 were inert towards radical cyclization, with the exception of N-benzyl-2-bromo-N,2-dimethylpropanamide (6b), which, upon treatment with Ni powder in i-PrOH, afforded the cyclized product 9b in low yield (Table 4). Upon irradiation, the extended anilides 6, 7, 10, and 11 yielded the corresponding dehydrobromination products exclusively (Table 5).