Tosylhydrazones elimination reactions

As a result, trisylhydrazones 95 allow the use of just 2 equivalents of alkyllithinm, and thus only a single equivalent of electrophile (E) is needed to trap the resultant vinyllithinm 97 to form the functionalized aUtene 98. Moreover, trisylhydrazone dianions 96 nndergo the elimination reaction much faster than do those derived from tosylhydrazones. This rate enhancement allows the use of even more acidic solvents, such as tetrahydrofuran. 

The reaction starts with formation of the tosylhydrazone from the epoxy-ketone. The tosylhydra-zone is unstable with respect to opening of the epoxide in an elimination reaction, and it is this elimination that sets up the familiar 1, 2, 3, 4 system ready for fragmentation. The push comes from the newly created hydroxyl group, and the pull from the irresistible concerted loss of a good leaving group (Ts ) and an even better one (N2). Notice how all the (green) bonds that break are parallel to one another, held anti-periplanar by two double bonds. Perfect ... 

Solvolysis can also occur from the diazonium salts derived from the intermediate diazocy-clopropanes. Ring opening of cyclopropyldiazonium salts accounts for the solvolysis products in Table 2, entries 8 and 9. Evidence for this is seen when sodium methoxide is replaced by the weaker base, sodium hydrogen carbonate, in which case only the methyl ethers derived from methanolysis were obtained. The a-elimination reaction of 1-cyclopropyl-1-nitrosourea with base likely involves diazocyclopropanes as intermediates which readily eliminate molecular nitrogen to form cyclopropylidenes. A more direct approach to diazocyclopropanes involves the Bamford-Stevens route via tosylhydrazones. Thus di-/er/-butylallene (19) was prepared from the tosylhydrazone of ( )-2,3-di-tert-butylcyclopropanone on treatment with base. ... 

The Shapiro reaction occurs when a tosylhydrazone 86, easily prepared from a ketone and tosylhydrazine, is treated with 2 equivalents of an ethereal solution of n-butyllithium 87, resulting first in the removal of the N—H proton to give the anion 88 and then of a one proton from the less-substituted a position to give the dianion 89. Elimination of lithium p-toluenesulfinate in the rate-limiting step gives the lithium aUtenyldiazenide 90, which suffers loss of nitrogen to afford the alkenyllithium 91 (equation 31) ° . ... 

Shapiro Reaction Treatment of the tosylhydrazone of an aldehyde or a ketone with a strong base leads to the formation of an olefin, the reaction being formally an elimination accompanied by a hydrogen shift. This reaction is called Shapiro reaction. 

The reduction of tosylhydrazones can also be performed with sodium borodeuteride in boiling methanol or dioxane, but the mechanism of this reaction (in boiling dioxane at least) is radically different from that of the lithium aluminum deuteride reductions.82 With sodium borohydride the first step is apparently hydride attack on the carbon atom of the C=N bond which is probably concerted with the elimination of the tosylate anion (110 - 111). Migration of the hydrogen from nitrogen to C-3 in (111) concerted with expulsion of nitrogen, provides the corresponding methylene derivative (100).82... 

A 2-cyclohexenone derivative can be transformed into the corresponding epoxy tosyl-hydrazone by sequential treatment with peracid and tosylhydrazine. The elimination of nitrogen and p-toluenesulfinate and fragmentation after rearrangement to the 3-tosylazo allylic alcohol may occur under mild conditions. Carbonyl compounds with 5,6-triple bonds are formed in high yields (J. Schreiber, 1967 M. Tanabe, 1967). If one applies this reaction to a 9,10-epoxy-1-decalone, a ten-membered 5-cyclodecyn-l-one ring is formed (D. Felix, 1971). This product is an important intermediate in the perfume industry and has been used on a large scale. For this purpose Eschenmoser developed a synthesis in which the readily removed styrene was split off instead of a sulfmic acid. Thus a l-amino-2-phenylaziridine hydrazone was used instead of a tosylhydrazone (D. Felix, 1968). ... 

Dehydroadamantanes are most readily obtained from either carbene insertion reactions or from 1,3-reductive eliminations. Pyrolysis of the dry sodium salt of the tosylhydrazone of adamantanone gives good yields of 2,4-dehydroada-mantane 133>. The unstable 1,3-dehydroadamantane is obtained from the treatment of 1,3-dibromoadamantane with sodium (Eq. (43)) 134>. 

The esters are prepared by reaction of the allylic or homoallylic alcohol with the tosylhydrazone of glyoxylic acid chloride- and N,N-dimethylaniline as a base, followed by elimination of /j-toluenesulfinic acid (triethylamine). Yields of —75% can be obtained. 

Treatment of a,p-unsaturated tosylhydrazones with NaBH4 in MeOH affords principally allylic ethers from cyclic derivatives and pyrazoles with most noncyclic examples. This divergent behavior compared to saturated tosylhydrazones has been attributedto a lessening of the electrophilicity of conjugated imine ir-bonds, which allows initial abstraction of the acidic N—H proton by BH4 to compete with reduction, and gives alternative reactions related to the Bamford-Stevens process as depicted in Scheme 4. An exception to this may be the deoxygenation of conjugated vinyl triflates (entry 11, Table 6). The cyclopropanation and elimination products produced in entry 4, Table 6 also probably arise from similar, alternative reaction paths. ... 

In contrast to these results, it has been demonstrated that a-(methylthio)tosylhydrazone monoanions, formed by reaction of an initially formed dianion with dimethyl disulfide, undergo in situ dianion formation rather than elimination, to give vinyl sulfides (Scheme 71 ). Since vinyl sulfides can be hydrolyzed to ketones, this sequence constitutes a very effective 1,2-carbonyl transposition. 

The reaction of alkyllithium reagents with acyclic and cyclic tosylhydrazones can lead to mixtures of elimination (route A) and addition (route B) products (Scheme 22). The predominant formation of the less-substituted alkene product in the former reaction (Shapiro Reaction) is a result of the strong preference for deprotonation syn to the N-tosyl group. Nucleophilic addition to the carbon-nitrogen tosyl-hydrazone double bond competes effectively wiA a-deprotonation (and alkene formation) if abstraction of the a-hydrogens is slow and excess organolithium reagent is employed. Nucleophilic substitution is consistent with an Su2 addition of alkyllithium followed by electrophilic capture of the resultant carbanion. 

Many more carbenes can be made safely from diazoalkanes if the diazoalkane is just an intermediate in the reaction and not the starting material. Good starting materials for these reactions are tosylhydrazones, which produce transient diazo compoimds by base-catalysed elimination of toluenesulfinate. The diazo compound is not normally isolated, and decomposes to the carbene on heating. 

A synthesis of alkynes from esters via a one-carbon homologation is by reaction with 1-lithiomethylbenzotriazole, followed by elimination of the derived benzotriazol-1-ylmethyl ketone tosylhydrazones. ... 

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