Synthesis and Mechanistic Study of Fused 2-Pyrrolines via Thermolysis of 6-Substituted-3,5-hexadienyl Azidoformates.

Thermolysis of 3,5-hexadienyl azidoformates at 300 °C, 0.05 Torr, led to a fused 2-pyrroline regiospecifically, regardless of the configuration E or Z between the C-3 and C-4 double bond. Thermolysis of 6-substituted-3,5(E)-hexadienyl azidoformates yielded a kinetically controlled 2-pyrroline with cis configuration between H-1 and H-8a whereas 6-substituted-3,5(Z)-hexadienyl azidoformates produced a cis and trans mixture. The mechanism was proposed as the loss of nitrogen to form an acyl nitrene, then addition to a double bond to produce an aziridine. Finally the cleavage of the C−C bond generated a vinylazomethine ylide followed by recyclization to a fused 2-pyrroline.