Tosylhydrazones elimination

Under acidic conditions, dienone tosylhydrazones 5 cyclize to 1 -tosyl-6,7-dihydro-l//-l,2-diazepines 6,l04a which on treatment with sodium ethoxide eliminate the elements of/Moluenesul-finic acid to yield an equilibrium mixture of the tautomeric 3//-1,2-diazepines 7 and 8.104b... 

Tosylhydrazones react with phenyltrimethylammonium tribromide under phase-transfer catalysed basic conditions to yield, initially, a-bromo- and derivatives which, under the basic conditions, eliminate one equivalent of HBr to yield unstable 2-tosylazopropenes [27]. 

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) ° . ... 

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. 

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. 

Carbenes are known intermediates in the thermolytic or photolytic decomposition of the lithium or sodium salts of tosylhydrazones, which, for endocyclic carbenes, results in ring contraction when the elimination of / - or y-hydrogens is impeded. Simple cyclobutanes generally cannot be prepared by this route from monocyclic cyclopentanone tosylhydrazones. However, the lithium salt of bicyclo[2.2.1]heptan-7-one tosylhydrazone gave bicyclo[3.2.0]hept-l-ene (4) as the major product (74%) by vacuum pyrolysis at 185 JC/20 Torr, together with bicyclo[2.2.1]heptane (14%) and tricyclo[2.2.1.02,7]heptane (12%) in 80% overall yield.67... 

Another route that has been recommended recently is oxidation of the As-stenyl acetate to the corresponding 7-kctone, conversion to the p-tosylhydrazone, and elimination with lithium hydride. Overall yields are in the range 20-50%.2... 

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... 

Many examples of natural furans are recorded as having been prepared from five-membered heterocycles such as 2(5H)-furanones (butenolides), which are reduced to furans with diisobutylaluminum hydride. The facile elimination of selenoxides derived from a-phenylseleneyl-y-lactones with formation of endocyclic a,/3-unsaturated butenolides is reported (75JOC542) as a useful route to 2,4- and 2,3,4-substituted furans via their corresponding butenolides. The mixture of dihydrofurans obtained from the tosylhydrazone of tetrahydro-2-furanone (Scheme 88) was oxidized to furans by 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (66CJC1083). 

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). ... 

Eschenmoser and collaborators (28) have reported the base induced fragmentation of a.B-epoxy-tosylhydrazones to produce acetylenic ketones (e.g. 69 71). Interestingly, in this fragmentation, both the triple-bond and molecular nitrogen are produced from the key intermediate 70 via an anti mode. The decarboxylation of nitrobenzisoxazole carboxylate (72) into 2-cyano-5-nitrophenol (73) can also be viewed as a trans-elimination (29, 30). 

The ketone 446 also served as a suitable starting material for the syntheses of ( )-montanine(415) and ( )-coccinine (413). Accordingly, the olefin 448 admixed with the A1 2 isomer was obtained from the tosylhydrazone 447 by base catalysed elimination. Bis-hydroxylation of the double bond of purified 448 achieved by the usual osmylation protocol... 

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>. 

Still other epoxide cleavage processes can be nucleophile induced, but without direct attack at a heterocyclic carbon. A good illustration of this phenomenon is seen in the alkylative elimination of epoxy tosylhydrazones (62). Optically pure allyl alcohols have been prepared... 

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 ... 

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. 

Two equivalents of a strong base such as n-butyllithium abstract first the tosylhydrazone proton and then the less acidic a-carbonyl proton, leaving a dianion A. The A eliminates first p-toluenesulfinate and then N2. The resulting vinyllithium compound B on protonation gives alkene (Scheme 4.54). 

The effect of a base is to convert the tosylhydrazone (8) into a diazo-alkane (9) and toluene- -sulphinate anion, in an a-elimination process represented by ... 

The attempted conversion of the aldehyde in compound (65) to a methyl group by reduction of the tosylhydrazone with NaBH4 (ethanol solvent) led instead to the furan derivative (66), resulting from an unusual cyclization with elimination of a MeOCH2 group. 

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. ... 

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