Diazo compounds diazoketones

Rhodium(II) acetate was found to be much more superior to copper catalysts in catalyzing reactions between thiophenes and diazoesters or diazoketones 246 K The outcome of the reaction depends on the particular diazo compound 246> With /-butyl diazoacetate, high-yield cydopropanation takes place, yielding 6-eco-substituted thiabicyclohexene 262. Dimethyl or diethyl diazomalonate, upon Rh2(OAc)4-catalysis at room temperature, furnish stable thiophenium bis(alkoxycarbonyl)methanides 263, but exclusively the corresponding carbene dimer upon heating. In contrast, only 2-thienylmalonate (36 %) and carbene dimer were obtained upon heating the reactants for 8 days in the presence of Cul P(OEt)3. The Rh(II)-promoted ylide formation... 

Intramolecular C/H insertion by copper-catalyzed decomposition of a-diazoketones provides a convenient cyclization procedure which is limited, however, to diazo compounds which allow energetically favorable realization of the transition state leading to the cyclized product. 

Abstract Diazonium salts have been previously used to cleave DNA via generation of carbon centered radicals and cations. Efforts have been made in the past decade or so to develop diazo compounds and a-diazoketones for physiologically relevant DNA cleavage. These efforts, coupled with their relevance to the mechanism of action of kinamycin and lomaiviticin antibiotics and other naturally occurring diazo compounds, will be discussed. 

Scheme 12 shows synthesis of 1,2,3-thiadiazoles by the Wolff, Hurd-Mori and Pechmann-Nold methods. Pechmann s and Wolffs are the oldest of the methods. The Pechmann-Nold synthesis involves the [3 + 2] cycloaddition of diazo-compounds to isothiocyanates or thiocarbonyl compounds (modified Pechmann synthesis). The use of thiocarbonyl compounds in the [3 + 2] cycloaddition step has broadened the scope of this reaction and made the starting materials more readily accessible. Wolffs method requires the synthesis of diazoketones that are treated with a thionating reagent to produce 1,2,3-thiadiazoles. With the development of new methods of diazotransfer reactions, the diazoketone precursors have become easily attainable and with further attention to the thionating reagents, this reaction is also useful for the synthesis of 1,2,3-thiadiazoles. 

There are several reports in the literature dealing with the bimolecular [3 + 2] cycloaddition reactions of alkynyl-substituted diazo compounds. Propargyl diazoacetate 212, when stored for 2 weeks at 0 °C, was transformed into an oligomer to which the constitution 213 was assigned (273) (Scheme 8.50). The alkynyl-diazoketone 214 requires a much higher temperature and is transformed into pyrazole 215, which probably arises from intermolecular cycloaddition, pyrazole tautomerization, and carbenic N/H insertion (274). The inter-intramolecular... 

Diazoketones react with trifluoromethyl hypofluorite to give a mixture of oc.a-difluoro ketones and a-fluoro-a-trifluoromethoxy ketones [70, 71] With elemental fluorine, two fluorine atoms replace the nitrogen in both diazoketones and unactivated diazo compounds [70, 72, 73] (equation 9)... 

The diazoketone explodes at 138—140°C, or on treatment with cone, sulfuric acid. See other DIAZO COMPOUNDS, NITROARYL COMPOUNDS... 

Certain diazoketones, for example diazopyruvate, alkyl 2-diazo-3-oxobutyrate or 3-diazo-2,4-pentanedione, react with vinyl ethers under metal catalysis to give dihydrofurans rather than cyclopropanes l Most work on this type of transformation has been that of Wenkert and Alonsoand their respective groups. A representative example is shown in equation 107. Finally, carbenoid dimerization is also a competitive reaction in metal catalysed intermolecular cyclopropanation. However, control of the chemoselectiv-ity to favour the cyclopropanation is possible. In general, the dimeric product can be avoided by using excess of alkene or by very slow addition of the diazo compound to a mixture of alkene and catalyst... 

According to the findings of kinetic and mechanistic studies of the hydrolysis reaction, the aliphatic diazo compounds may be divided into the following three groups (a) ethyl diazoacetate, primary diazoketones, primary diazosulfones, 2,2,2-trifluorodiazoethane (b) diaryldiazo-methanes, 9-diazofluorene and ring substituted derivatives, p-nitrophenyl-... 

These findings are not surprising since the alpha carbon atoms of these diazo compounds carry an aromatic ring. However, it has been observed recently by Dahn et al. [210] that solvent isotope effects are larger than 1 in the acid catalyzed hydrolyses of various secondary diazoketones (such as 3-diazo-2-butanone), ethyl a-diazopropionate, and l,l,l-trifluoro-2-diazopropane. Similar results have been obtained by Jugelt and Berseck... 

In Scheme 42.4 the diazoketone operates in a third mode. Here the diazo compound acts as an electron donor, the dominant process when it is exposed to protic or Lewis acids. The resulting intermediate XVIII then becomes... 

As olefinic substrates a,j -unsaturated carbonyl compounds (esters, anhydrides, ketones, quinones), nitriles and nitro compounds can be used. The rate of addition of the diazo compounds is dependent upon the nature of the diazo compound and generally the following order of reactivity can be observed diazomethane > diphenyldiazomethane > methyl diazoacetate > diazoketones. 

Neutral diazo compounds such as diazoketones, diazoacetates and diazomethane are efficient alkylating agents with weakly acidic... 

Dehydroalanine 116 desmosine 48, 49 diazo compounds 157 aryl diazonium salts, reactive properties 157 synthesis 160 diazoacetates, analysis of products 165 reactive properties 162 synthesis 164 diazoketones, analysis of products 162 conversion to haloketones 139 reactive properties 165 synthesis 140 diazomethane preparation 141 reactive properties 162 diazonium salts 89 diazonium-IH-tetrazole 90, 95 3,4-dihydroxyproline 52, 53 diimidoesters 69 diisopropylfluorophosphate 130 2,3-dimethylmaleic anhydride 83 dinitrophenylation 79 disulfide bond reduction 103... 

Rhodium(II) acetate was found to be much more superior to copper catalysts in catalyzing reactions between thiophenes and diazoesters or diazoketones The outcome of the reaction depends on the particular diazo compound With f-butyl... 

Diazo compounds, most commonly diazoesters or diazoketones, are the reagents of choice for metal-catalyzed cyclopropanation of alkenes (Eq. 1) [31]. Of the two, diazoesters, and particularly ethyl diazoacetate (EDA), are the more frequently used in synthesis. 

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