Ketones, reductive cleavage Wolff-Kishner reduction

This silyl hydrazone formation-oxidation sequence was originally developed as a practical alternative to the synthesis and oxidation of unsubstituted hydrazones by Myers and Furrow [31]. The formation of hydrazones directly from hydrazine and ketones is invariably complicated by azine formation. In contrast, silyl hydrazones can be formed cleanly from /V,/V -bis(7< rt-butyldimethylsilyl)hydrazine and aldehydes and ketones with nearly complete exclusion of azine formation. The resulting silylhydrazones undergo many of the reactions of conventional hydrazones (Wolff-Kishner reduction, oxidation to diazo intermediate, formation of geminal and vinyl iodides) with equal or greater efficiency. It is also noteworthy that application of hydrazine in this setting may also have led to cleavage of the acetate substituents. 

Ganter has developed three different approaches to tricyclo[5.2.1.0 ]decane (403), yet another of the nineteen isomeric hydrocarbons of adamantaneland As seen in Scheme XXXIII, the routes involve intramolecular cyclization of keto tosylate 399 followed by Wolff-Kishner reduction of the resulting ketone, thermo-cyclization of 400 and subsequent dechlorination, hydrogenation, and photocycli-zation of aldehydes 401. Majerski s approach involved hypoiodite cleavage of alcohol 402... 

Direct transition from level 2 to level 0 can be achieved by way of the Wolff-Kishner reaction (treatment of the respective hydrazones with alkali), a classical pathway for the reduction of carbonyl compounds. At the same time, a direct conversion of aldehydes and ketones into alkenes is also feasible via reductive cleavage of their tosylhydrazones under the action of MeLi, the Shapiro reaction (Scheme 2.63). "... 

Wolff-Kishner reduction with cyclopropyl cleavage) of a 9/3,19-cyclo-ii-ketone S. M. Kupchan, E. Abushanab, K, T. Shama-sundar and a. W. By, J. Am. Chem. Soc., 89 (1967) 6327. 

The method has now been used to synthesize 9,10-dimethyl-trarcs-l-decalones,11 which have the characteristic C/D ring system of pentacyclic triterpenes. Thus i ruction of the hydroxy enol ether (9) with the Simmons-Smith reagent gives the cyclopropyl ether (10). Cleavage with 7% methanolic hydrochloric acid leads to the hydroxy ketone (11), convertible by Wolff-Kishner reduction followed by oxidation into (12). 

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