A. Roy et al., Anionic [4+2] cycloaddition reactions of dihydropyrazolin-5-one dienolate with dienophiles: a novel approach for substituted and fused indazolones, J CHEM S P1, (20), 1999, pp. 3001-3004
Dihydropyrazolin-5-one dienolate 2 generated by deprotonation of 2,3-dimeth
yl-4-formyl-1-phenylpyrazolin-5-one (4-formylantipyrine) is shown to be an
efficient anionic pyrazolone alpha-oxy-o-quinodimethane analog, which under
goes facile cycloaddition with a variety of dienophiles to give substituted
indazolones in good yields after dehydration-dehydrogenation of cycloadduc
ts.