On the reactivity of some 2-methyleneindolines with b-nitroenamines, a-nitroalkenes, and 1,2-diaza-1,3-butadienes

A study of the behaviour of some electron-rich 2-methyleneindolines (1–3) with different electron-poor reagents (formation of new carbon–carbon and nitrogen–carbon bonds) has furnished interesting results from both synthetic and the mechanistic viewpoints. Enamines 1–3 have been reacted with the β-nitroenamines 4–7 (reaction CeCl3·7H2O promoted), giving the polymethine dyes 14–23. The same bases 1–3 have been nitroalkylated with the nitroolefins 8–10, furnishing the indolines 24–32, and the diastereoselectivity of the reaction has been thoroughly investigated. The most unexpected results derived from the first example of reaction of Fischer's bases with 1,2-diaza-1,3-butadienes. In fact, with 11–13, the ‘unknown’ indoline spirodihydropyrroles 33–40 were formed. Their structures were unambiguously assigned, and we determined, as an example, that of 33 by X-ray analysis.