Inverse and Normal [4 + 2] Cycloadditions of a 4a,8a‐Methanophthalazine to Azirines and 1,2,4‐Triazoline‐3,5‐dione as Heterodienophiles

The 4a,8a‐methanophthalazine 4 is a novel propellane containing an electron‐rich cyclohexadiene and an electron‐deficient diazadiene system within the same molecule. The highly strained azirines 6 and 9a–c, prepared from the corresponding vinyl azides 5 and 8a–c, undergo cycloaddition in situ to the diazadiene system of 4 to furnish the stable polycyclic azo compounds 7c and 10–12 which possesses exo configuration at the annulated aziridine. Attack apparently occurs from the less hindered face, anti to the methano bridge of 4 with high stereo‐ and site selectivity. The electron‐deficient 1,2,4‐triazoline‐3,5‐dione 13 reacts with the electron‐rich diene of the azo compound 12 to yield the anti‐anti bisadduct 14.