Pericyclic Domino reactions with 3,6-Bis(trifluoromethyl)-1,2,4,5-tetrazine: A convenient entry into azo cage compounds
作者:Thilo Klindert、Peter von Hagel、Luzian Baumann、Gunther Seitz
DOI:10.1002/prac.199733901111
日期:——
3,6-Bis(trifluoromethyl)-1,2,4,5-tetrazine (1) characterized by a highly reactive, electron deficient diazadiene system reacted with several cyclic and acyclic bis-dienophiles to yield the cage compounds 11, 19a,b, 31a,b and 41 in a pericyclic homo-domino reaction in good yields. The first step of the domino reactions is an inverse electron demand intermolecular Diels-Alder addition followed by elimination of nitrogen to give 4,5-dihydropyridazines which then undergo a terminaI ring closure to yield the cage compounds. The solvent employed and the reaction temperature is of crucial importance. Whereas in nitromethane and at elevated temperatures the main products are the cage compounds, at lower temperature and in dichloromethane as solvent the initially formed 4,5-dihydropyridazines are frequently converted to 1,4-dihydropyridazines by a 1,3-H-shift. Treatment of the tetrazine 1 with cyclooctatriene 23 did not lead to a cage compound in any case; instead via valence tautomeric species octa-1,3,5,7-tetraene 23a and bicyclo[4.2.0]octa-2,4-diene 23b the twofold pyridazine-substituted butadienes 24 and 26 together with the tricyclic cyclobuta[f]phthalazine 25 were formed.