Unexpected behavior of the reaction between 1,2-diaza-1,3-butadienes and 3-dimethylaminopropenoates: a useful entry to new pyrrolines, pyrroles, and oxazolines |
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Authors: | Attanasi Orazio A Favi Gianfranco Filippone Paolino Golobic Amalija Stanovnik Branko Svete Jurij |
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Institution: | Istituto di Chimica Organica, Università degli Studi di Urbino Carlo Bo, Via Sasso 75, 61029 Urbino, Italy. |
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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. |
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