On the reactivity of some 2-methyleneindolines with β-nitroenamines, α-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 CeCl 3 ·7H 2 O 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.