title: Unexpected behavior of the reaction between 1,2-diaza-1,3-butadienes and 3-dimethylaminopropenoates: a useful entry to new pyrrolines, pyrroles, and oxazolines.
abstract: We observed a nucleophilic attack by the ene-amino carbon of 3-dimethylaminopropenoates at the terminal carbon of the azo-ene system of 1,2-diaza-1,3-butadienes. In tetrahydrofuran at 65 degrees C, this attack produced 1-aminopyrrolines with a high degree of cis-stereoselectivity by means of an unusual zwitterionic adduct intermediate followed by intramolecular ring closure. In toluene under reflux, 1-aminopyrrolines produced oxazoline-fused 1-aminopyrrolines. Oxazoline-fused 1-aminopyrrolines were directly obtained by reaction of 1,2-diaza-1,3-butadienes with 3-dimethylaminopropenoates in toluene under reflux. The ring opening of oxazoline-fused 1-aminopyrrolines in acidic or basic media provides highly substituted 1-aminopyrroles. 5-Unsubstituted 1-aminopyrrole derivatives were obtained from 1-aminopyrrolines under basic conditions by loss of dimethylamino and ester groups. We discuss the plausible mechanisms of the ring closure and opening.
authors.affiliation: Istituto di Chimica Organica, Università degli Studi di Urbino Carlo Bo, Via Sasso 75, 61029 Urbino, Italy.
authors.forename: Orazio A
authors.initials: OA
authors.lastname: Attanasi
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Favi
authors.forename: Paolino
authors.initials: P
authors.lastname: Filippone
authors.forename: Amalija
authors.initials: A
authors.lastname: Golobic
authors.forename: Branko
authors.initials: B
authors.lastname: Stanovnik
authors.forename: Jurij
authors.initials: J
authors.lastname: Svete