Unsaturated carbonyl compounds Lead tetraacetate

Phosphomolybdic acid-Potassium di-chromate-Copper(II) sulfate, 248 Tin(II) trifluoromethanesulfonate, 301 Other unsaturated carbonyl compounds Lead tetraacetate, 155 Pyrylium perchlorate, 263 Zinc-copper couple, 348 a-Substituted-a, p-unsaturated carbonyl compounds... 

The 2,3-dihydro-l//-pyrazole obtained from the reaction of hydrazine with an a-)8-unsaturated carbonyl compound will sometimes give a sufficient proportion of the 4,5-dihydro-3i/-pyrazole tautomer at equilibrium so that it is possible just to heat the 1//-tautomer to eliminate nitrogen and form a cyclopropane. In other cases, it is necessary to reduce the 1//-tautomer and oxidize back to the 3 -form. It is also possible to use the conversion of the H- to the 3//-tautomer to introduce substituents at C3 of the 4,5-dihydro-3//-pyrazole and hence into the cyclopropane. The reaction of 4-methylpent-3-en-2-one with hydrazine gave 2,2,4-trimethyl-2,3-dihydro-lH-pyrazole (1). Treatment with lead tetraacetate gave the 3-acetoxy derivative 2 and on thermolysis, l-acetoxy-l,2,2-trimethylcyclopropane (3). Alternatively, tosylation and reaction with methyllithium gave 3,3,5,5-tetramethyl-4,5-dihydro-3//-pyrazole (4) which on thermolysis or photolysis gave 1,1,2,2-tetramethylcyclopropane route to tetramethylcy-... 

Trimethylsilyl azide, (TMSN3) reacts with carbon-carbon double bonds to form a compound which can be cleaved by lead tetraacetate (or phenyliododiacetate) to yield a carbonyl and a nitrile, as in equation (37).The reagent has been tqrplied extensively to the cleavage of unsaturated steroids, as illustrated in equation (38). 

Oximes react with lead tetraacetate (one-half equivalent) in acetic acid at 70° (1 hr.) to give the corresponding carbonyl compound in 60-90% yield. The reaction can even be applied to unsaturated oximes if an equivalent amount of anhydrous... 

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