2,3,7-triazabicyclo[3.3.0]octenes prepared by tandem cascade reaction of allyl azides and olefinic dipolarophiles

Tandem cascade reactions of allyl azides 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 diazo ester (4) and then an intramolecular dipolar cycloaddition from the diazo functional group and the double bond in 4 to give 5. Compound 5 may furthermore 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 suitable solvent or an appropriate temperature.