Arylsulfonylhydrazones

Although the present procedure illustrates the formation of the diazoacetic ester without isolation of the intermediate ester of glyoxylic acid />-toluenesulfonylhydrazone, the two geometric isomers of this hydrazone can be isolated if only one molar equivalent of triethylamine is used in the reaction of the acid chloride with the alcohol. The extremely mild conditions required for the further conversion of these hydrazones to the diazo esters should be noted. Other methods for decomposing arylsulfonyl-hydrazones to form diazocarbonyl compounds have included aqueous sodium hydroxide, sodium hydride in dimethoxyethane at 60°, and aluminum oxide in methylene chloride or ethyl acetate." Although the latter method competes in mildness and convenience with the procedure described here, it was found not to be applicable to the preparation of aliphatic diazoesters such as ethyl 2-diazopropionate. Hence the conditions used in the present procedure may offer a useful complement to the last-mentioned method when the appropriate arylsulfonylhydrazone is available. 

Aryloxyalkylacetonitriles, 49, 17 Aryloxyalkylisothiouronium salts, 49,17 Aryloxyalkyl thiocyanates, 49, 17 Arylsulfonylhydrazones, decomposition by base, 49, 26... 

Intermediate diazonium ions as precursors of carbocations which can rearrange in the manner discussed are also formed in the photolyses of arylsulfonylhydrazones in basic medium. The photolysis of the optically active bicyclo[2.2.1]hept-5-en-2-one tosylhydrazone in 0.5 M sodium hydroxide gave bicyclo[3.1.1]hept-3-en-2-ol (25) in 6% yield with only 5% of retention of the optical activity, which indicates an achiral ally cation as the product-determining intermediate.84... 

Direct alkylation of 5-substituted tetrazoles is often the best method of obtaining simple 2,5-disubstituted tetrazoles. The 1,5-isomers, which are formed as competitive side products, are usually separated with ease by fractional crystallization or better by column chromatography on alumina or silica gel which gives excellent separations of most tetrazole isomers (8UCR(S)174). Another convenient synthesis of 2,5-disubstituted tetrazoles (241) is the formazan method (Scheme 31). By coupling aldehyde arylsulfonylhydrazones (240) with diazonium salts in basic solutions, compounds (241) may be obtained directly in yields of up to 78% (76BCJ1920). 

REDUCTION OF ALDEHYDE AND KETONE ARYLSULFONYLHYDRAZONES WITH HYDRIDE REAGENTS... 

Conversion of ketones into arylsulfonylhydrazones allows preparation of the corresponding vinyl I ith iums by base-prom oted decomposition of the hydrazone. This is known as the Shapiro reaction. 

The base catalyzed decomposition of arylsulfonylhydrazones of aldehydes and ketones to provide alkenes is called the Bamford-Stevens reaction. When an organolithium compound is used as the base, the reaction is termed the Shapiro reaction. The most synthetically useful protocol involves treatment of the substrate with at least two equivalents of an organolithium compound (usually MeLi or BuLi) in ether, hexane, or tetramethylenediamine. The in s/ft formed alkenyllithium is then protonated to give the alkene. The above procedure provides good yields of alkenes without side reactions and where there is a choice, the less highly substituted alkene is predominantly formed. Under these reaction conditions tosylhydrazones of a,(3-unsaturated ketones give rise to conjugated dienes. It is also possible to trap the alkenyllithium with electrophiles other than a proton. 

Kurek-Tyriik, A., Marozak, S., Michalak, K., Wicha, J., Zarecki, A. Reaction of Arylsulfonylhydrazones of Aldehydes with a-Magnesio Sulfones. A Novel Olefin Synthesis. J. Org. Chem. 2001, 66, 6994-7001. 

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. 

As noted above, the classical Shapiro reaction requires the use of >2 equiv of base to effect the conversion of an arylsulfonylhydrazone to an alkene. However, in recent work Yamamoto has described a catalytic version of the Shapiro reaction that employs aziridinyl hydrazones and is effective with only 5-30 mol% of added base.21 As shown above, treatment of hydrazone 34 with 5 mol% of LDA affords a 93% isolated yield of 35 with >99 1 stereoselectivity. This reaction is believed to proceed via metalation of 34 with LDA to yield 36. This intermediate decomposes with loss of styrene and nitrogen to provide vinyllithium reagent 37, which is protonated by diisopropylamine, regenerating the LDA base. Unfortunately this method is not amenable to the capture of the intermediate vinyllithium species with electrophiles. 

The arylsulfonylhydrazone 18 is a stable precursor of the cyelohexadienyllithium 7. In order to prepare this starting reagent, 3-acetoxymethyl-2,4-dimethyl-1,3-penta-diene 12 is subjected to a Diels-Alder reaction with the ketene equivalent ehloro-acrylnitrile 11a. The cyeloadduct 16 primarily obtained is hydrolyzed to the hyd-roxyketone 17 in i-butyl alcohol. Subsequent reaction with /-butyldimethylsilyl-chloride (TBSCl) and imidazole in dichloromethane serves to protect the primary aleohol function of the intermediate 10 in which the keto carbonyl group is deriva-tized to the required arylsulfonylhydrazone 18 with 2,4,6-triisopropylphenylsul-fonylhydrazide in tetrahydrofuran (THF) as solvent. 

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