Phenyl carbene, from decomposition

The 4,5-corane (84) is obtained in SOX yield on photo-decarbonylation of the pentacyclic ketone (85). Photochemical decomposition of the carbonate (86), by the loss of carbon dioxide, affords a mixture of products containing oxirane. styrene oxide, bibenzyl and phenylacetaldehyde. Triplet sensitized irradiation yields products solely from benzyl radicals. - An earlier study of the irradiation (at 254 nm) of the carbonate (87) reported that benzaldehyde, phenyl carbene, and carbon dioxide were produced. A reinvestigation of the irradiation of this compound (at 254 nm in acetonitrile) has provided evidence that the cis- and trans-stilbene oxides (88) and (89) are formed as well as deoxybenzoin and smaller amounts of diphenylacetaldehyde and bibenzyl. When methanol is used as the solvent the same products are produced accompanied by benzylmethyl ether, 1,2-diphenylethanol, and 2,2-diphenylethanol. These authors suggest that the oxiranes (88) and (89) are formed by way of... 

Obtained from active methylene compounds, such as malonic esters, -0x0 esters and jS-oxo sulfones, iodonium ylides serve as precursors of the corresponding carbenes. Their decomposition by a catalytic amount of a copper salt in the presence of a C-C double bond has been used for inter- and intramolecular cyclopropanation reactions. Thus, reaction of cyclohexene with bis(methoxycarbonyl)methylene(phenyl)iodine(III) under the catalytic action of bis(acetylacetonato)copper(II) yielded dimethyl bicyclo[4.1.0]heptane-7,7-dicarboxylate (1) (38%, mp 91-93°C) in addition to tetrakis(methoxycarbonyl)ethene (41%). ... 

New evidence as to the nature of the intermediates in catalytic diazoalkane decomposition comes from a comparison of olefin cyclopropanation with the electrophilic metal carbene complex (CO)jW—CHPh on one hand and Rh COAc) / NjCHCOOEt or Rh2(OAc)4 /NjCHPh on the other . For the same set of monosubstituted alkenes, a linear log-log relationship between the relative reactivities for the stoichiometric reaction with (CO)5W=CHPh and the catalytic reaction with RhjfOAc) was found (reactivity difference of 2.2 10 in the former case and 14 in the latter). No such correlation holds for di- and trisubstituted olefins, which has been attributed to steric and/or electronic differences in olefin interaction with the reactive electrophile . A linear relationship was also found between the relative reactivities of (CO)jW=CHPh and Rh2(OAc) NjCHPh. These results lead to the conclusion that the intermediates in the Rh(II)-catalyzed reaction are very similar to stable electrophilic carbenes in terms of electron demand. As far as cisjtrans stereoselectivity of cyclopropanation is concerned, no obvious relationship between Rh2(OAc) /N2CHCOOEt and Rh2(OAc),/N2CHPh was found, but the log-log plot displays an excellent linear relationship between (CO)jW=CHPh and Rh2(OAc) / N2CHPh, including mono-, 1,1-di-, 1,2-di- and trisubstituted alkenes In the phenyl-carbene transfer reactions, cis- syn-) cyclopropanes are formed preferentially, whereas trans- anti-) cyclopropanes dominate when the diazoester is involved. 

Silanes can react with acceptor-substituted carbene complexes to yield products resulting from Si-H bond insertion [695,1168-1171]. This reaction has not, however, been extensively used in organic synthesis. Transition metal-catalyzed decomposition of the 2-diazo-2-phenylacetic ester of pantolactone (3-hydroxy-4,4-dimethyltetrahydro-2-furanone) in the presence of dimethyl(phenyl)silane leads to the a-silylester with 80% de (67% yield [991]). Similarly, vinyldiazoacetic esters of pantolactone react with silanes in the presence of rhodium(II) acetate to yield a-silylesters with up to 70% de [956]. 

Treatment of the title compound with an aqueous base under phase-transfer catalysis conditions generates, by a-elimination, chloro(trifluoromethyl)carbene that can be trapped by cycloaddition to allylsilane and allylstannane derivatives, e.g. formation of 1 and 2. This method represents a fast and mild alternative to the Seyferth method that starts from the same alkyl halide and generates the carbene by thermal decomposition of l-bromo-l,2,2,2-tetra-fluoroethyl(phenyl)mercury (see Section 1.2.1.2.4.1.1). 

Bis(alkylthio)carbenes (59) generated by thermal decomposition of the corresponding oxadiazolines have been added to phenyl and vinyl isocyanates to form substituted lactams (60) in good yields. The methodology proved to be compatible with many functionalities. Moving from the bis(alkylthio)carbenes to carbenes derived from ephedrine and methylaminoindanol allowed the development of an asymmetric version of this reaction which provides an efficient route to both enantiomers of hydroisatin (61). ... 

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