2,3,7‐Triazabicyclo[3.3.0]octenes Prepared by Tandem Cascade Reaction of Allyl Azides and Olefinic Dipolarophiles

Tandem cascade reactions of allylazides and olefinic dipolarophiles to give cis‐fused 2,3,7‐triazabicyclo [3.3.0]octenes (5, 6 or 7) are reported. Therein, an intermolecular dipolar cycloaddition of azide and alkene gave a triazoline which was followed by isomerization of the triazoline to a diazoester (4) and then an intramolecular dipolar cycloaddition from the diazo functional group and the double bond in 4 to give 5. Compound 5 may further more undergo a Michael addition to give 7‐substituted‐ 2,3,7‐ triazabicyclo [3.3.0]oct‐2‐ene (6) or a tautomerization to give 2,3,7‐triazabicyclo[3.3.0]oct‐3‐ene (7). The reaction may be manipulated to stop at a particular stage by adopting a suit able solvent or an appropriate temperature.