Tosylhydrazones alkenes from

A more promising procedure for the formation of alkenes from tosylhydrazones is represented by the Shapiro reaction It differs from the Bamford-Stevens reaction by the use of an organolithium compound (e.g. methyl lithium) as a strongly basic reagent ... 

Alkene synthesis. A modified version of an earlier synthesis of alkenes from the tosylhydrazones of aldehydes and certain alkyllithium reagents (9, 472-473) employs the N-r-butyldimethylsilyl derivatives (1) of tosylhydrazones of a,f)-enals, which undergo only 1,2-addition of an alkyllithium at - 78°. The adducts (2) decom-... 

In situ reduction of tosylhydrazones by NaBHjCN provides an efficient method for the deoxygenation of carbonyl compounds to furnish the corresponding hydrocarbons (see also Section 3.4). In the case of tosylhydrazones derived from a,P-unsaturated carbonyl compounds, the reduction leads to a stereoselective migration of the double bond to give the corresponding tran -alkene. 

Scheme 26 illustrates the general reaction for the generation of alkenes from p-toluenesulfonylhydra-zones (tosylhydrazones). 

A general synthesis of fused methylenecyclopropanes employs the carbenoid ring contraction of bicyclic cyclobutanone tosylhydrazones, available from [2-1-2] cycloaddition of dichloro-ketene to alkenes. ... 

In particular, sulfonylhydrazones are valuable coupling partners in Pd-catalyzed cross-coupling reactions with aryl halides and pseudohalides giving rise to alkenes. As an example, the reaction of a chloroarene with the tosylhydrazone derived from 4-tert-butylcyclohexanone leads to an aryl substituted cyclohexenone (Experimental Procedure below). " " Moreover, the reaction can be conducted directly from the carbonyl... 

Thermal decomposition of y-lactone tosylhydrazone sodium salts are reported to yield cyclobu-tanones, which can be accounted for by rearrangement of an intermediate oxycarbene. In this manner, the sodium salts of dihydrofuran-2(37/)-one tosylhydrazones 1 were decomposed as a loose powder, at 310 C in a bulb-to-bulb distillation apparatus at an initial pressure of 0.1 Torr, to give the corresponding cyclobutanones 2 in addition to enol ethers, cyclopropanes and open-chain alkenes. Condensable products (74-76%) were collected at — 78 °C, weighed and the ratio of components was determined from their relative GC peak areas.63... 

The reaction of p-chlorobenzaldehyde with phenyldiazomethane in the presence of (MeOlsP and catalytic amounts of meso-tetraphenylporphyrin iron chloride (ClFeTPP) resulted in the formation of the corresponding alkenes with an /Z-selectivity of 86 14, but the yield was low (30%). When phenyldiazomethane is generated in situ from the corresponding potassium tosylhydrazone salt, the olefin yield increases to 92% with E/Z-selectivity of 97 3. Thus, high levels of -selectivity are obtained with semistabilized ylides by this method . This process is applied to a wide range of aldehydes and is practical as compared to standard Wittig reaction, and therefore finds applications in industry, o... 

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). "... 

Mechanistic information on the photolytic Bamford-Stevens reaction is provided by the successful isolation of a diazo hydrocarbon as a reaction intermediate from the direct photolysis of a tosylhydrazone sodium salt (90 Scheme 10). This study also clarifies that the carbene derived thermally and that derived photolytically behave differently with respect to the stereoselectivity of the 1,2-hydrogen shift that produces the alkene. 

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). 

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. 

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. 

Related carbenes, i.e. 3//-benzocycloheptatrien-3-ylidene and 5/7-dibenzo[a,c]cycloheptatrien-5-ylidene generated from the corresponding tosylhydrazones, thermally or photolytically, isomerize to benzo-12 or dibenzobicyclo[4.1.0]hepta-2,4,6-trienes, respectively. In contrast to cycloheptatrienylidene, 5/7-dibenzo[a,c]cycloheptatrien-5-ylidene underwent ring contraction to form a cyclopropene derivative 13 before reaction with alkenes. 

Another transannular reaction, which likewise proceeds via carbene insertion, is the base-catalyzed decomposition of the tosylhydrazone of cyclooctanone. In general these carbenes react with a- and -C—H bonds to give alkenes and cyclopropanes. However, when the carbene carbon can approach distant C —H bonds, such as in the cyclooctane conformation, then bicyclo[3.3.0]octane derivatives are also formed from transannular insertion.Thus, cyclooctanone- and 5-phenylcyclooctanone tosylhydrazones reacted with sodium methoxide to give a mixture of mono- and bicyclic products 4-6 and 7-10, respectively, in the stated proportions. 

The Shapiro reaction1 is the conversion of arylsulfonylhydrazones to alkenes via treatment with alkyllithium reagents or alkali metal amides.2,3,4,5 The reactions proceed via alkenyllithium intermediates, which can be transformed to the alkene upon protonation or can be captured with other electrophilic reagents. For example, the tosylhydrazone 1 derived from 2-methylcyclohexanone was converted to 3-methylcyclohexene (2) in 98% yield upon treatment with two equivalents of butyllithium.1... 

The base-mediated conversion of arylsulfonylhydrazones to alkenes was first observed by Bamford and Stevens in 1952.6 In a representative transformation, tosylhydrazone 3 was converted to cyclohexene (4) in quantitative yield after refluxing for 90 minutes in an alkoxide solution derived from dissolution of sodium in ethylene glycol. These reactions are believed to proceed via intermediate diazo compounds, which are transformed to alkenes by thermal elimination processes. 

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