Alkenes from ketone tosylhydrazones

Decomposition of a diazoalkene in the presence of an alkene either by thermolysis," " photolysis or in the presence of transition metals " generates a vinylcyclopropane. The diazo compound can be isolated or formed in situ from the tosylhydrazone of an a, -unsaturated aldehyde or ketone. 

Fig, 8 Synthesis of alkenes through coupling of heterocyclic tosylhydrazones with aryl halides, (a) reaction from hydrazone (b) reaction from ketone... 

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). "... 

When the vinyllithium intermediate (190) is treated with water, the procedure provides a useful synthetic method for the conversion of ketones to alkenes (Scheme 79). The method is illustrated by the conversions of the tosylhydrazones of phenyl isopropyl ketone (194) and dipropyl ketone (195) to the alkenes (196) and (197), respectively (Scheme 79). In this method, experiments have demonstrated that the hydrogen is derived from the water, as indicated in Scheme 79, and thatTMEDA is an excellent solvent. The vinyllithium intermediate (190) may be trapped by other electrophiles thus, with carbon dioxide and DMF, the reaction affords ,[i-unsaturated carboxylic acids and aldehydes like (198) and (199) (Scheme 80). 

Tosylhydrazones of aliphatic aldehydes and ketones react with a base in an aprotic solvent at 90-180 C to give diazo compounds which undergo thermal decomposition with loss of nitrogen to yield alkenes derived from hydrogen migration and cyclopropanes from intramolecular insertion. In proton donor solvents decomposition of y-tosylhydrazones by base occurs primarily by a cationic mechanism involving diazonium and/or carbenium ion intermediates. 

In most cases the regiochemistry of the Shapiro reaction is controlled by steric factors, with the second metalation occurring at the less-substituted a-carbon atom of the hydrazone.2 For example, a-methyl ketone 10 was transformed to disubstituted alkene 11 in 69% yield as a single regioisomer via conversion to a tosylhydrazone followed by treatment with -BuLi. However, the regiochemical outcome of Shapiro reactions involving a,p-unsaturated hydrazones is difficult to predict in the absence of data obtained from reactions of structurally related substrates, as the second metalation can occur at either the a - or y-position. 

The conversion of ketone 38 to alkene 40 in the context of Winterfeldt s synthesis of (-)-myltaylenol was accomplished in two steps using classical conditions for the Shapiro reaction.22 The tosylhydrazone 39 was generated cleanly from 38 in near quantitative (98%) yield. Treatment of 39 with excess n-BuLi provided 40 in 90% yield. 

Xanthenyliumsodium (from sodamide and xanthene) reacts with aziridines to give a mixture of 9-mono- (271) or 9,9-di-substituted xanthenes (272).Addition of perchloric acid to unsymmetric allenes such as the 9-xanthylidene derivative (273) (prepared by a new route from 9,9-dichloroxanthene and an alkene) gave a red xanthylium salt (274), which was converted into a colourless spiro-indene (275) on heating.Full details have now been published of the properties and of the reactions of 9-diazoxanthene (276) and 9-xanthylidene (278) with methyl acrylate, substituted styrenes, several ketones, and alkyl-benzenes. The kinetics of the reaction with styrenes were studied and the conversion of (276) into (278) was achieved by photolysis of the tosylhydrazone (277) at —25 °C. 

Shapiro reaction. (2, 418-419 6, 598-600). Several laboratories have used EDA instead of an alkyllithium for decomposition of tosylhydrazones of ketones to olefins. Trisubstituted alkenes can be prepared by this modification in moderate yields from tosylhydrazones that contain only tertiary a-hydrogens. This modification also favors formation of the (Z)-disubstituted olefin. ... 

Reduction of a unsaturated tosylhydrazones. Hutchins et al. reported briefly that reduction of tosylhydrazones of aliphatic a,/8-unsaturaled ketones produces alkenes resulting from migration of the double bond to the carbon originally bearing the carbonyl group. Taylor and Djerassi have since examined this reduction in detail with steroidal substrates and found that the situation is more complex. Thus reduction of the tosylhydrazone of A -cholestenone gives the four products shown in equation (I). Reduction of the tosylhydrazone of A - -cholestadienone-3 is even more complex (equation II). 

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