A novel synthesis of 3-nitroindoles via electrocyclization of 2,3- (dialk-1-enyl)-4-nitropyrroles

Article abstract of DOI:10.1016/S0040-4020(97)10405-7

3-Nitroindoles (10) are prepared in good yields via a thermal 6π- electrocyclization of 2,3-(dialkenyl)-4-nitropyrroles (4) in nitrobenzene, a solvent which causes in situ aromatization of the initially formed dihydroindoles (8). The corresponding reaction of 2-alkenyl-3-alkadienyl-4- nitropyrroles (5) also leads to 3-nitroindoles (11), however, now together with 3-nitrotetrahydroindole derivatives (12). The latter compounds are formed by a tandem 6π-electrocyclization-intramolecular Diels-Alder reaction, and are the predominant (or only) products when nitrobenzene is replaced by triglyme.