[4 + 2] Cycloaddition Reactions of a 4a,8a‐Methanophthalazine with Electron‐Rich Alkynes: A New Synthesis of Substituted 1,6‐Methano[10]annulenes

The novel propellane 3 containing an electron‐rich cyclohexadiene and an electron‐deficient diazadiene system in one and the same molecule reacts site selectively with the electron‐rich alkynes 4 and 8 as well as with cyclooctyne (10) to yield the interestingly substituted novel 1,6‐methano[10]annulenes 7, 9, and 11. In contrast to this course of reaction, benzyne (12) undergoes a cycloaddition with the cyclohexadiene moiety of 3 with high site selectivity anti to the methano bridge to furnish the pentacyclic pyridazine derivative 14. Interestingly benzyne (12) is able to react with the diazadiene system of the phthalazine 17 to form the triptycene 19 via the azo compound 18.