Diazocarbonyl oxidations

Bethell and Wilkinson, 1970) and that, therefore, a diazocarbonyl oxide (9.73), and even its cyclization product 9.74, may be intermediates before the release of dinitrogen. 

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. 

Rhodium(II) acetate catalyzes C—H insertion, olefin addition, heteroatom-H insertion, and ylide formation of a-diazocarbonyls via a rhodium carbenoid species (144—147). Intramolecular cyclopentane formation via C—H insertion occurs with retention of stereochemistry (143). Chiral rhodium (TT) carboxamides catalyze enantioselective cyclopropanation and intramolecular C—N insertions of CC-diazoketones (148). Other reactions catalyzed by rhodium complexes include double-bond migration (140), hydrogenation of aromatic aldehydes and ketones to hydrocarbons (150), homologation of esters (151), carbonylation of formaldehyde (152) and amines (140), reductive carbonylation of dimethyl ether or methyl acetate to 1,1-diacetoxy ethane (153), decarbonylation of aldehydes (140), water gas shift reaction (69,154), C—C skeletal rearrangements (132,140), oxidation of olefins to ketones (155) and aldehydes (156), and oxidation of substituted anthracenes to anthraquinones (157). Rhodium-catalyzed hydrosilation of olefins, alkynes, carbonyls, alcohols, and imines is facile and may also be accomplished enantioselectively (140). Rhodium complexes are moderately active alkene and alkyne polymerization catalysts (140). In some cases polymer-supported versions of homogeneous rhodium catalysts have improved activity, compared to their homogenous counterparts. This is the case for the conversion of alkenes direcdy to alcohols under oxo conditions by rhodium—amine polymer catalysts... 

Silver salts are well established to promote atom transfer reactions.1-5 In 1946 Bachmann and coworkers reported that silver oxide facilitated the Wolff rearrangement6 of a-diazocarbonyl compounds.7 After this initial report, several other silver(I) reagents (including AgN03 and Ag02CPh)8,9 were identified to provide higher yields,... 

The same salt from acetylene afforded similarly adducts with furan and 1,3-diphenyl i sobenzofuran. A number of alkynyl iodonium salts underwent also [2 + 3] cycloaddition with dipolarophiles such as a-diazocarbonyl compounds, nitrile oxides, etc., allowing the preparation of iodonium salts with an alkenyl or a heterocyclic moiety [7],... 

Such studies have, thus far, been restricted to the reactions of selected alkynyliodonium salts with limited sets of nitrile oxides, nitrones, diazocarbonyl compounds and organo-... 

Copper powder, copper bronze, copper(I) oxide, copper(II) oxide, copper(Il) sulfate, and cop-per(I) halides, typically applied as a suspension in refluxing solvent or alkene, are used extensively for intermolecular cyclopropanation with diazoacetic esters or diazomalonic esters, and for intramolecular cyclopropanation of unsaturated diazocarbonyl compounds. Bis(acetylacetonato)copper(Il) [Cu(acac)2], a more recently introduced catalyst, is only sparingly soluble in the typical solvents and alkenes which are used and is therefore applied under the same conditions. Catalysts such as trialkyl phosphite and triaryl phosphite complexes of copper(I) halides and salicylaldimatocopper(II) chelates [e.g. 1 (R = (R)-a-phenylethyl, R = /ert-butyl ) and 2 ] are soluble in many organic solvents and liquid alkenes. 

The strongly polarized C = C bond of alkynyliodonium salts, along with their propensity for Michael additions, predicts that they should be good 1,3-dipolarophiles. Indeed, reaction of arylethynyliodonium tosylates with arenenitrile oxides, 127, gives a mbtture of cycloadducts, 128 and 129, in 62-80% yields [91] [Eq. (59)]. Similarly, Me3SiC=CIPh OTf and various diazocarbonyl compounds, 130, result [92] in cycloadducts 131 [Eq. (60)]. Likewise, alkynyliodonium salts react with methyl and phenyl azide to give low yields of triazines, 132, as adducts [Eq. (61)]. 

Diazocarbonyl and diazophosphoryl compounds react with silver (ii) oxide easily (Schollkopf and Rieber, 1969). In diazomethane, both H-atoms are replaced with silver acetate in a mixture of ether and pyridine (Blues et al., 1974). Mono- and disilver diazo compounds are often used for C-alkylation (see examples given by Regitz and Maas, 1986, Sect. 14.6). 

Regitz and Maas (1986, Table 14.5) give 23 further examples of diazomethyl alkylation with aldehydes and ketones. A potential difficulty may be the dimerization of diazocarbonyl and related compounds in the presence of alkali hydroxides, by which l,4-dihydro-l,2,4,5-tetrazines are formed (see the discussion in Sect. 9.2). We know, however, of only one case in which this reaction interfered (Disterdorf and Regitz, 1976 diazomethyl(diphenyl)phosphine oxide, (H5C6)2P(0) —CH=N2). 

Metallocarbene precursors other than diazocarbonyls have been examined sporadically for the generation of oxonium ylides, though not in the context of complex target synthesis. Among these, iodonium ylides and oxidative activation of allqnies in the presence of gold catalysts have shown significant promise. 

Unlike diazocarbonyl compounds, most aromatic azides are reasonably stable and can be carried through multistep syntheses that do not involve excessive heating, or strong oxidizing or reducing conditions. 

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