Reactions Involving Diphenyldiazomethane

The mechanism of this type of esterification reaction has been much studied in recent years, using diphenyldiazomethane. In alcoholic solvents the mechanism of the reaction involves a rate-determining proton transfer from the acid to the carbon atom of the diazoalkane, to form a benzhydryldiazonium-carboxylate ion-pair135, viz. 

The results in the diazomethane reactions involving zinc(II) chloride catalysis have been explained by invoking a carbenoid intermediate. The properties of such a species will, of course, be sensitive to the nature of the metal and this might explain the different regioselectivity observed when diphenyldiazomethane is decomposed with rhodium and palladium salts in the presence of 5-methylenebicyclo[2.2.1]hept-2-ene (9). With rhodium(II) acetate as catalyst the exocyclic double bond is attacked exclusively, whereas palladium(II) chloride catalysis directs cyclopropanation to the endocyclic double bond. ... 

The reaction of diazoalkanes with acetylenes can give rise to cyclopropenes by two main routes. Some reactions involve an initial loss of nitrogen to generate a carbene which then adds to the acetylene (see Section 1.2.1.), but this section is concerned only with those reactions where the first step is a cycloaddition leading to formation of a 3//-pyrazole. Unlike the parallel series of reactions in the cyclopropane series, where the C-C double bond of the alkene requires activation by a suitable substituent or by strain. Under pressure even acetylene itself will react with diazoalkanes. For example, diphenyldiazomethane underwent addition in good yield and deazetization gave 3,3-diphenylcyclopropene (1). ... 

Treatment of the diselenocyclic allene shown with diphenyldiazomethane in refluxing benzene affords 2,2-diphenyl-1,3-selenane 46 in modest yield (Equation 6) <2001JOC7202>. Presumably, the reaction involves a complex series of diphenyldiazomethane additions, losses of nitrogen, and rearrangements. Irradiation of the diallene shown affords the acetylenic diselenane 47, again in modest yield (Equation 7) <2001JOC1787>. 

The elusive diazoalkenes 6 and 14 are unlikely to react with methanol as their basicity should be comparable to that of diphenyldiazomethane. However, since the formation of diazonium ions cannot be rigorously excluded, the protonation of vinylcarbenes was to be confirmed with non-nitrogenous precursors. Vinyl-carbenes are presumedly involved in photorearrangements of cyclopropenes.21 In an attempt to trap the intermediate(s), 30 was irradiated in methanol. The ethers 32 and 35 (60 40) were obtained,22 pointing to the intervention of the al-lylic cation 34 (Scheme 10). Protonation of the vinylcarbene 31 is a likely route to 34. However, 34 could also arise from protonation of photoexcited 30, by way of the cyclopropyl cation 33. The photosolvolysis of alkenes is a well-known reaction which proceeds according to Markovnikov s rule and is, occasionally, associated with skeletal reorganizations.23 Therefore, cyclopropenes are not the substrates of choice for demonstrating the protonation of vinylcarbenes. 

The preparation of thiiranes is most conveniently performed in solution. However, there are also protocols reported for reaction in the gas and solid phase. By using diazo and thiocarbonyl compounds in ether as solvent, both alkyl and aryl substituted thiiranes are accessible. As indicated earlier, aryl substituents destabilize the initially formed 2,5-dihydro-1,3,4-thiadiazole ring and, in general, thiiranes are readily obtained at low temperature (13,15,35). On the other hand, alkyl substituents, especially bulky ones, enhance the stability of the initial cycloadduct, and the formation of thiiranes requires elevated temperatures (36 1,88). Some examples of sterically crowded thiiranes prepared from thioketones and a macro-cyclic diazo compound have been published by Atzmiiller and Vbgtle (106). Diphenyldiazomethane reacts with (arylsulfonyl)isothiocyanates and this is followed by spontaneous N2 elimination to give thiirane-2-imines (60) (107,108). Under similar conditions, acyl-substituted isothiocyanates afforded 2 1-adducts 61 (109) (Scheme 5.23). It seems likely that the formation of 61 involves a thiirane intermediate analogous to 60, which subsequently reacts with a second equivalent... 

The second mechanism (A—SE2) involves a rate-determining proton transfer to carbon and general acid catalysis is observed. The mechanism is illustrated in (31) for the hydrolysis of ethyl diazopropionate in aqueous buffers (IIA/A-). The overall reaction can be followed spectrophoto-metrically and fen a will be the observed second-order rate coefficient. Compounds of the type N2 CR CO R, with R = OEt, Me or Ph and R = Me, Et, iso-Pr or Ph [53] as well as diphenyldiazomethane [51] (Ph2C=N=N) are decomposed according to (31). The products of reaction vary somewhat depending upon the diazo compound. 

The electrophilic cyclopropane 59 is prepared according to a reaction scheme which involved the photolysis of ethyl diazoethylidenecyanoacetate (56) to give the cyclopropene (57) derivative which in turn on addition of diphenyldiazomethane afforded the bicyclic pyrazoline (58). Thermolysis of 58 produced bicyclo[ 1.1.0]butane derivative 59 (equation 9). ... 

Most preparations of cyclopropanes involving catalytic decomposition of diaryldiazomethanes have been carried out by using zinc(II) chloride. The best result was achieved when diphenyldiazomethane was decomposed in the presence of ethyl vinyl ether at 25 °C l-ethoxy-2,2-diphenylcyclopropane was isolated in 52 /o yield.In general, the yield of the cyclopropane is sensitive to the temperature at which the reaction is carried out the lower the temperature, the lower the amount of the cyclopropane. Thus, when zinc(II) chloride catalyzed decomposition of diphenyldiazomethane was carried out in the presence of cyclopentadiene, the yield of 6,6-diphenylbicyclo[3.1.0]hex-2-ene (4) drops from 35 /o to 23"/o when the temperature is lowered from 22 °C to <... 

The involvement of trimethylenemethane diradicals in deazetization of diazoalkane-allene adducts or trimethylene diradicals in the deazetization of the adducts of acyclic alkenes often leads to mixture of regioisomers and stereoisomers and from the standpoint of cyclopropane syntheses, this is undesirable. Far fewer problems of this type attend deazetization of the adducts of cyclic or polycyclic alkenes and, furthermore, even a modest amount of strain in the system activates the alkene to diazoalkane addition so that there is no need for activating substituents on the double bond. Cyclopropene is highly reactive towards diazoalkanes (see also Section 1.1.5.1.5.3.1.) and cycloaddition reactions of this type provide a ready entry into the bi-cyclo[1.1.0]butane series. The addition of diphenyldiazomethane to cyclopropene gave 4,4-diphenyl-2,3-diazabicyclo[3.1.0]hex-2-ene (1), which on photolysis gave a mixture of 2,2-diphenylbicyclo[1.1.0]butane (2) and 1,1-diphenylbuta-l,3-diene (3). ... 

Nucleophilic substitution reactions may involve several different combinations of charged and uncharged species as reactants. The equations in Scheme 4.1 illustrate the four most common charge types. The most common reactants are neutral halides or sulfonates, as illustrated in Parts A and B of the scheme. These compounds can react with either neutral or anionic nucleophiles. When the nucleophile is the solvent, as in Entries 2 and 3, the reaction is called a solvolysis. Reactions with anionic nucleophiles, as in Entries 4 to 6, are used to introduce a variety of substituents such as cyanide and azide. Entries 7 and 10 show reactions that involve sulfonium ions, in which a neutral sulfide is the leaving group. Entry 8 involves generation of the diphenylmethyl diazonium ion by protonation of diphenyldiazomethane. In this reaction, the leaving... 

The addition of ethyl diazoacetate and diphenyldiazomethane to dibutyl vinyl-boronate was first reported over forty years ago [87]. This initial study was completed later to establish the scope and limitations of these reactions and the exact nature of the intermediates involved [88]. The regioselective cydoaddition step was immediately followed by a spontaneous 1,3-migration of boron to give a N-boronyl 2-pyrazo-line, which can be trapped, after hydrolysis, with phenylisocyanate (Scheme 9.41). 

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