From diazoalkanes with

No matter how they are generated, carbenes and carbenoids undergo four typical reactions. The most widely used reaction is cyclopropanation, or addition to a TT bond. The mechanism is a concerted [2 + 1] cycloaddition (see Chapter 4). The carbenes derived from chloroform and bromoform can be used to add CX2 to a 7T bond to give a dihalocyclopropane, while the Simmons-Smith reagent adds CH2. Carbenoids generated from diazoalkanes with catalytic Rh(II) or Cu(II) also undergo cyclopropanations. 

It appears to be a stable covalent highly crystalline compound (unlike other metal methanediazoates). Alkanediazoates are easily converted to diazoalkanes, so should be regarded as capable of detonation. (Though named by the author as a methanedia-zoate, it is indexed and registered in CA as a nitrosomethylamide salt) [1], A sample of the freshly synthesised compound was dissolved in dichlorodideuteromethane and sealed into an NMR tube. Four days later, when the tube was being opened for recovery of the sample, the tube exploded. This was attributed to diazomethane formation, possibly from reaction with traces of moisture sealed into the tube [2], See other heavy metal derivatives, n-o compounds... 

As in experiments with diazirine 1, the maximum yields of the ylides, and hence of the carbenes, increased with increasing strength of the alkyl group s a-CH bond.56 For example, the relative yields of carbene 45 from diazoalkane photolysis were 100% for R=cyc/o-C3H5, 96% for R=t-C4H9, and 72% for R=CH3 the relative carbene yields decreased to 14% with R=C2Hs and to only 7% with R=i-C3H7. 

RIES from diazoalkanes is also sensitive to the dihedral angle between the migrating a-H and the C-N bond of the diazo moiety.57 For example, the A values for the pyridine capture of the photolytically generated carbenes from 46 and 47 are in the ratio of 1.7 1. Similarly, the carbene from 46 is more efficiently generated and trapped in methanol, whereas the photolysis of 47 in methanol affords twice as much olefin (by 1,2-H RIES) compared to the photolysis of 46. These phenomena are attributed to conformational factors that favor RIES during the photolysis of 47, with the proximal excited state represented as a pyramidalized 1,3-C-N=N diradical.57... 

Metallic groups as in case (c) lead to electrophilic or even carbocation-like carbene complexes. Typical examples are Fischer-type carbene complexes [e.g. (CO)5Cr=C(Ph)OMe] and the highly reactive carbene complexes resulting from the reaction of rhodium(II) and palladium(II) carboxylates with diazoalkanes. Also platinum ylides [1,2], resulting from the reaction of diazoalkanes with platinum(Il) complexes, have a strong Pt-C o bond but only a weak Pt-C 7t bond. In situation (d) the interaction between the metal and the carbene is very weak, and highly reactive complexes showing carbene-like behavior result. Similar to uncomplexed carbenes. 

It has been known for a long time that the decomposition of diazoalkanes can be catalyzed by transition metal complexes [493-496]. Carbene complexes were proposed as possible intermediates by Yates in 1952 [497]. However, because reactions of diazoalkanes with metal complexes tend to be difficult to control, it was not until 1975 [498] that stable carbene complexes could be directly obtained from diazoalkanes (Figure 3.19). 

Functionalized zinc carbenoids have been prepared from diiodoalkanes and diethylzinc and used in stereoselective transformations, but their use is limited by the availability of the diiodoalkane" ° and the stability of the resulting zinc carbenoid. Alternatively, the reaction of a diazoalkane with Znl2 can be used to access complex zinc carbenoids, but with modest efficiency (equation 9) . ... 

Azines, derived from two moles of diazoalkane with loss of nitrogen, have been observed as byproducts by several authors.11,53,71... 

Cycloaddition of diazoalkanes with thiocarbonyl compounds occurs usually in the regiochemistry derived from a thiophilic addition of the carbon end of the dipole to sulfur, yielding a 1,3,4-thiadiazoline (1). 

A number of other diazocompounds have been studied. Warren (1961) has shown that the reaction of 9-diazofluorene in ethanol and in ethanol-water mixtmes is similar to that of diphenyldiazomethane. The rate of reaction is slower in deuteriated solvent and the operation of general acid catalysis was inferred from measurements with picric acid. As would be expected from the conjugation between the diazo and dibenzo-cyclopentadienyl groups in 13, the rate of reaction is slower than that of DDM (by a factor of about twelve) and there seems little doubt that both substrates react with a rate-determining proton transfer. Bate studies with substituted diazofluorenes yield a value of — p = l 6-l-9 depending on the substituent constants used (Warren, 1963 Warren and Yandle, 1965). This value is similar to that for the reaction of substituted diphenyldiazomethanes in toluene and is a further indication that the stability of diazoalkanes is quite sensitive to substituent effects. 

Because the rate-determining step for the reaction of diazoalkanes with acids varies from substrate to substrate and with reaction conditions, the discussion of rate- and product-determining steps cannot be wholly separated. The steps involving and following the loss of nitrogen will now be considered. The reason for making a division at this point is that diazonium ions are formed in a number of reactions and, to understand their behaviour, it is helpful to consider information from various sources. A considerable part of this section will, therefore, be devoted to reactions other than those of diazoalkanes themselves. 

The reaction is especially suited to the generation of optically active diazonium ions with specifically oriented counter-ions. In this respect it has possibilities which are absent for the reaction of diazoalkanes with acids and the deamination of aliphatic amines. However, in carrying out stereochemical studies, great care must be exercised to avoid spurious results, since the transient formation of a diazoalkane, either by loss of a proton from the diazonium ion or by what is probably a concerted elimination reaction of the diazoester, can lead to racemisation of the alkyl function and loss of asymmetry in the anion. Moreover, the diazoester is liable to nucleophilic displacement, for example by an acid molecule formed from already rearranged nitrosoamide, and this can lead to inverted product. 

In contrast to the wealth of chemistry reported for catalyzed reactions of diazocarbonyl compounds, there are fewer applications of diazomethane as a carbenoid precursor. Catalytic decomposition of diazomethane, CH2N2, has been reported as a general method for the methylenation of chemical compounds [12]. The efficacy of rhodium catalysts for mediating carbene transfer from diazoalkanes is poor. The preparative use of diazomethane in the synthesis of cyclopropane derivatives from olefins is mostly associated with the employment of palladium cat-... 

Condensation with carbonyl compounds. Formation of epoxides from aldehydes by reaction with sulfonium ylides is subject to asymmetric induction. The latter species have been generated from 91, 92, and 93, and also those derived from monoterpenes, e.g., 94 " and 95.- Of course the ylides can be obtained in situ by deprotonation of sulfonium salts or copper-catalyzed decomposition of diazoalkanes (with the carbenoids trapped by the sulfides). 

The first step in the decomposition of nitrosoamides 123) is formation of the diazo ester 125) which fragments to a diazonium ion pair (128)129 The ion pairs thus produced differ from those obtained in the reaction of diazoalkanes with acids. The ratio of ester to ether formed in the decomposition of rV-nitroso-fV-benzhydrylbenz-amides in alcohol is lower than that found in the reaction of diphenyldiazomethane 132) with acids, and in the solvolysis of benzhydryl benzoate (I35)135,136 This effect has been attributed to the intervention of trans-diazo ester in the decomposition of 125) which leads to a greater distance between carbocation and carbox-ylate anion. In the diazoalkane reaction attack of the acid occurs at the electron-rich carbon atom to generate the carboxylate in the immediate vicinity of the incipient carbocation. 

Table 3. Bicyclo[1.1.0]butanes from Reaction of Diazoalkanes with Cyclopropenes...

Aryl-l-methylquinazolinium salts (111) also reacted with diazomethane. In this case, however, two molecules of diazoalkane could react with the quinazolinium salt. In anhydrous medium at 10°C the 1,2-dihydro adduct (112) was formed together with a 1 1 mixture (24% yield) of the benzodiazepines 113 and 114. At lower temperatures —45°C), on the other hand, 114, from reaction with two molecules of diazomethane, was the only product... 

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