Dipolar Cycloaddition Reactions of Diazoazoles with Electron-Rich and with Strained Unsaturated Compounds

Article abstract of DOI:10.1021/jo00234a008

Regiospecific net 1,7-cycloaddition reactions of electron-rich or strained olefins and electron-donor acetylenes occur readily (-70 to -10 degC) with diazoazoles having nitrogen in the 2-positions of their azole rings.Diazoazoles such as 5-tert-butyl-3-diazo-3H-pyrazole (20), 3-diazo-5-phenyl-3H-pyrazole (24), 2-diazo-2H-imidazole (28), 4,5-dicyano-2-diazo-2H-imidazole (12), 4-diazo-4H-imidazole (63), 4-diazo-5-phenyl-4H-1,2,3-triazole (70), 5-cyano-4-diazo-4H-1,2,3-triazole (74), 3-diazo-3H-1,2,4-triazole (76), and 3-diazo-5-phenyl-3H-1,2,4-triazole (79) thus usually add effectively to unsaturated reactans such as enamines, 1-alkoxyalkenes, ketene acetals, aryl isocyanates, norbornene, and norbornadiene to give new 1,7-cycloadducts.These cyclization reactions may be followed by tautomerization processes leading to new stabilized fused heterocycles or by elimination to novel highly delocalized heteroaromatic derivatives. 4,5-Dicyano-2-diazo-2H-imidazole (12) undergoes various accelerated cycloadditions to unsaturates and adds to norbornene and norbornadiene by exclusive exo dipolar processes.Addition of activated acetylenes to representative α-diazoazoles also results in regiospecific 1,7-cyclization to give stabilized fused azolo heterocycles.