Carbenes, from tosylhydrazones

The generation of carbenes from tosylhydrazones of thiophene aldehydes, and their reactivity have been discussed in CHEC-I, <84CHEC-I(4)74i>. A few further reactions of such carbenes have been reported. In presence of acrylonitrile, the product could be either the cyclopropane (484) (from the carbene) or the pyrazoline (485) (by cycloaddition of the diazo intermediate) <88H(27)ll4i>. The carbene can similarly be trapped by cis and trans stilbene, dimethyl fumarate or maleate to form the respective cyclopropanes <87BCJ4317>. 

The pyrolysis of tosylhydrazones 14 and 16 obtained from the corresponding ketones yields tricyclic products 15 and 17, respectively, via carbenic intermediates. Generation of the carbenes from 14 and 16 leads to preferential 1,3-migration of the trimethylsilyl group to the carbenic... 

Interactive mechanism for carbene formation from tosylhydrazones... 

Bamford-Stevens and Shapiro Reactions. The Bamford-Stevens reaction is used to obtain unsaturated compounds from tosylhydrazones. A base is required to generate its monoanion, which thermally decomposes to yield the corresponding di-azo derivatives. These reactive species evolve to give an aUcene through carbenium ions in protic solvents or carbenes in aprotic solvents. The thermal decomposition of the monoanions of trisyl-hydrazones is commonly used to obtain diazoalkanes for different applications such as functionalization of solid supports, epox-idation and alkenylation of aldehydes, or the study of radicals and carbenes The functionalization of a Merrifield resin with... 

Weak base such as cesium carbonate has been utilized in this reaction to generate diazo compounds in situ from tosylhydrazones through the Bamford-Stevens reaction. The reaction is initiated by palladium-promoted decarboxylation of propargylic carbonate to form propargylpalladium complex A, which then tautomerizes to afford allenylpalladium intermediate B. Subsequently, the common carbene formation-migratory insertion-p-hydride elimination occurs to afford various vinylallenes (Fig. 30). 

This chapter focuses on the generation of carbenes by extrusion of nitrogen (Tables 91.1 through 91.8). Several other methods are possible, such as the formation from tosylhydrazone salts, oxiranes, aziridines, dioxolanes, and pyrazolenines from cyclopropanes by photocydoehmination, from transition-metal carbene complexes or by a-elimination, from ot,a-dihalogen compounds, or from base treatment of N-nitrosocarbamate. ... 

Thermolysis and/or photolysis of tosylhydrazone salts, accessible by condensation of p-toluene-sulfonyl-hydrazine with aldehydes or ketone, gives rise to elimination of the sulfinate salts and forms the intermediate diazo compound (Scheme 18). Generation of free carbenes by this method is sometimes in doubt and, as a consequence, this method is not included in this chapter except when generation of a carbene from the diazirine or diazo compound is not available. 

Scheme 7.43 Catalytic epoxide (X=0), aziridine (X=AZ-Ts or AZ-SES), and cyclopropane (X=CH-COY) formation mediated by chalcogen-ylides generated from metal carbenes using diazo compounds generated in situ from tosylhydrazones (start at lower right)...

The l,3-dithian-2-ylidene substituted carbene (54), accessible from the tosylhydrazone (53) by a Bamford - Stevens reaction, not only participates in cycloaddition reactions but is also a source of 4,8-dithiaspiro[2.5]oct-l-ene 6JCS(P1)2773>. 

Scheme 6.114, a carbene-carbene rearrangement transforms diphenylcarbene to o-phenylphenylcarbene, which is the progenitor of 565. Two phenylbicydo[4.1.0]-hepta-2,4,6-trienes and l-phenyl-l,2,4,6-cycloheptatetraene (562) have to be assumed as further intermediates. The participation of 562 is supported by the structure of the products 563 and 564, which should result from the addition of 562 to diphenylcarbene and the dimerization of 562, respectively. By thermolysis of the sodium salt of 2-phenyltropone tosylhydrazone, 562 was generated directly. At 100 °C in diglyme as solvent, 564 was identified as the only product and at 340°C/4Torr in the gas... 

Throughout this chapter, we have almost always ignored the role of the carbene precursor. Carbenes are generally made from diazo compounds, or from a variety of surrogate diazo compounds including diazirines, tosylhydrazone salts, and aziridyl imines, all of which probably decompose through nonisolable diazo compounds. Not surprisingly, it turns out that diazo compounds have a rich chemistry of their own, especially when irradiated. Moreover, that chemistry often closely resembles the reactions of carbenes. Much of intramolecular carbene chemistry is, in fact, diazo compound chemistry. 

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... 

Phenyl(trimethylsilyl)carbene (21) has been generated from phenyl(trimethylsilyl)diazo-methane (20) by gas-phase pyrolysis39,40 as well as by thermolysis97 or photolysis33,40,98,99 in solution, by flash thermolysis of the tosylhydrazone lithium salt 18040, and by pyrolysis... 

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>. 

C6o reacts with diazomethane to yield fulleroids [97,99,100,234], Carbene generated from the thermolysis of precursors such as diazirines, sodium trichloroac-etate, cyclopropene, oxadiazole, and tosylhydrazone [60,235] adds onto C6o leading to methanofullerenes [12,15,236], Recently, Akasaka et al. described the photochemical reaction of diazirine with C6o [237], Irradiation of a benzene solution of 2-adamantane-2,3 -[3H]-diazirine 58 and C6o with a high pressure mercury lamp (cutoff <300 nm) at 15°C in a Pyrex tube resulted in the formation of mixture of the isomers 59a and 59b in a ratio of 51/49 (Scheme 24). 

The thermal decomposition of monoanions of tosylhydrazone (Ar = p-tolyl) in a protic solvent like diglyme at 130°C or higher temperature generates dialkyl carbenes. Dialkyl carbenes can also be generated photochemically from salts of tosylhydrazones, but it is difficult to perform the reaction on a large scale. 

The 11-membered ring carbene was generated by thermolysis recently. To ensure coplanarity a brigded precursor such as 4.9-methano (11) annulenone-tosylhydrazone was used to give thus 4.9-methano (11) annulenylidene 6 39). The isomeric annulenylidene was synthesized from the tosylhydrazone of 1.6-methano-annulene-2-carboxaldehyde 39). 

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