Diketones, acid catalyzed with hydrazines

Diketones are synthetically quite versatile, but they have found only modest use in the syntheses of heterophanes. When 1,3-cyclohexadecanedione (53) is treated with hydrazine hydrate or phenylhydrazine, pyrazolophane (54) or (55), respectively, is obtained (78TL2821). Reaction of dione (56) with hydroxylamine, followed by acid-catalyzed cyclization of the intermediate monoxime, gives the [3,5]isoxazolophane (57) (79TL1875). 

The first synthetic reports on cycloalkynes involved a base-catalyzed oxidative decomposition of bis-hydrazones, readily prepared from the respective precursor 1,2-cycloalkadiones by condensation with hydrazine (Fig. 1, top). As oxidant, mercury oxide is most typically applied, however Ag20 or Pb(OAc)4 are also suitable. An analogous procedure (Fig. 1, bottom) employs the tosylate (Ts) derivative of hydrazine, which upon condensation with the diketone under reflux conditions forms the tosylated aminotriazole intermediate. Acidic removal of the tosyl group, followed by lead-mediated oxidation, also forms the desired cycloalkyne ring. 

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