Intramolecular 1,3-Dipolar Cycloaddition of Nitrilimines Bearing Alkenyl Groups

Article abstract of DOI:10.1246/bcsj.55.2456

The reaction of the arylhydrazones of some 2-(alkenyloxy)benzaldehydes(or 1-naphthaldehydes) with Pb(OAc)4 leads, via the nitrilimine intermediates, to intramolecular 1,3-dipolar cycloadducts, 3-substituted 2-aryl-2,3,3a,4-tetrahydro<1>benzopyrano(or naphtho<1',2':5,6>pyrano)<4,3-c>pyrazoles, in 10-80percent yields.In the presence of an excess of Pb(OAc)4, these cycloadducts were dehydrogenated to 3-substituted 2-aryl-2,4-dihydro<1>benzopyrano(or naphtho<1',2':5,6>pyrano)<4,3-c>pyrazoles.In the presence of a large excess of Pb(OAc)4, some of the pyrazoles were acetoxylatedto give the corresponding 4-acetoxypyrazoles.The effect of substituents of the alkenyl group on reactivity of the reaction was interpreted in terms of the frontier molecular orbital (FMO) theory.