Synthetic exploitation of the ring-opening of 3,4-dinitrothiophene, IX - Pyrrolidines, pyrrolines and pyrroles from 1,4-diaryl-2,3-dinitro-1,3-butadienes via a 5-endo-trig cyclization

The reactions between 1,4-diaryl-2,3-dinitro-1,3-butadienes 1a-d and primar y alkylamines gave high yields of N-alkyl-2,5-diaryl-3-alkylamino-4-nitropy rrolidines 2 as pure all-trans diastereomers via an unusually favoured 5-en do-trig ring closure. The stereochemistry of compounds 2 has been attribute d through an X-ray crystal structure analysis of the acetyl derivative 5 of 2ai. Amine elimination from 2 gave the N-alkyl-2,5-diaryl-3-nitro-3-pyrrol ines 3 which could be easily aromatized to the corresponding pyrroles 4.