Diazomethane isomeric compounds

Only two monoprenylated flavanones have so far been identified from Dorstenia species. As we have mentioned earlier 78 was obtained from the thermal reaction of 4-hydroxylonchocarpin (47). Twigs of D. poinsettifolia yielded dorspoinsettifolin (79). Cyclization of 48 in formic acid and methylation of 78 with diazomethane both readily gave 79. An isomeric compound, 6-methoxyisolonchocarpin, has been reported from Lonchocarpus subglauscescens [61]. 

The [3 + 2] cycloadduct formed on treatment of tetrakis(trifluoromethyl)-Dewar-thiophene with trifluoromethyl diazomethane isomerizes to give an annulated 3-trifIuoromethyl-l//-2-pyrazoline in the presence of acids and bases. Sulfur can be removed from both compounds on reaction with triphenylphosphine (80JA6633). 

The two isomeric compounds 1-chloropyrido[3.4-rf]pyridazin-4(3//)-one and 4-chloropyrido-[3,4-(/]pyridazin-1(2//)-one in dimethylformamide on addition of an ethereal solution of diazomethane both give 4 1 mixtures of the respective 0-methyl and A-methyl compounds 12/13 and 14/15.136... 

The energy difference between diazirine and diazomethane, interesting from the point of view of their isomerism, came from MS measurements (63JCP(39)3534). The appearance potentials of the CH2 ion, common to both compounds, yielded a difference in heats of formation of 125kJmor A strong peak in the mass spectrum of 3-chloro-3-methyl-diazirine (50) with relative mass 55 was ascribed to the methyldiazirinium ion (51). 

Prinzbach and Limbach have studied the valence isomerism between N-substituted azepines 14b and benzeneimines 14c (76CB3505) although 14b is much more stable (actually it is the only form detected by NMR), the compound could react, depending on R, as 14c with diazomethane. Later, Prinzbach et al. reported the study of the equilibrium 14b (90% )/14c (10%) in the case of R = p-tosyl [the compound has the following C-substituents 3,6-dichloro-4,5-di(methoxycarbonyl)] in the solid state (X-ray) only 14b is present [86CB616],... 

Addition of diazomethane to cyanoallene took place at the internal C=C bond of the cyanoallene to give 4-methylenepyrazoline 85. The following isomerization via 1,3-hydrogen shifts afforded 4-methyl-5-cyanopyrazole 86 [83], a-Diazo carbonyl compounds reacted in an analogous way [84]. 

Unexpected reaction products were obtained when compound 206 was treated with diazomethane. After initial methylation of the enol, ring opening and isomerization of the secondary amine to the imine follows, furnishing compound 207 in good yield (Equation 69) <2002JOC6971>. 

Diazo compounds also undergo cycloaddition with fullerenes [for reviews, see (104),(105)]. These reactions are HOMO(dipole)-LUMO(fullerene) controlled. The initial A -pyrazoline 42 can only be isolated from the reaction of diazomethane with [60]fullerene (106) (Scheme 8.12) or higher substituted derivatives of Ceo (107). Loss of N2 from the thermally labile 42 resulted in the formation of the 6,5-open 1,2-methanofullerene (43) (106). On the other hand, photolysis produced a 4 3 mixture of 43 and the 6,6-closed methanofullerene (44) (108). The three isomeric pyrazolines obtained from the reaction of [70]fullerene and diazomethane behaved analogously (109). With all other diazo compounds so far explored, no pyrazoline ring was isolated and instead the methanofullerenes were obtained directly. As a typical example, the reaction of Cgo with ethyl diazoacetate yielded a mixture of two 6,5-open diastereoisomers 45 and 46 as well as the 6,6-closed adduct 47 (110). In contrast to the parent compound 43, the ester-substituted structures 45 and 46, which are formed under kinetic control, could be thermally isomerized into 47. The fomation of multiple CPh2 adducts from the reaction of Ceo and diazodiphenylmethane was also observed (111). The mechanistic pathway that involves the extrusion of N2 from pyrazolino-fused [60]fullerenes has been investigated using theoretical methods (112). 

Trimethylsilylcyclopropenes also undergo regioselective addition of diazomethane 248,247) and rearrangement to the diazo-compound 247). Catalytic decomposition of the latter can lead to bicyclobutanes or to isomeric silyldienes, eg. ... 

This acid is a mixture of cis- and trans-isomers. By esterifying the acid to the methyl ester with diazomethane a two compound mixture is formed, whereas ester formation under acidic conditions (MeOH/HCl) gives a single compound. This single compound 115 is thought to be the trans-isomer, because isomerization of the mixture of esters obtained by reaction with diazomethane to a single compound is apparently possible by an esterification relactonization mechanism by treating the mixture with acid in methanol. These results are consistent with the formulation of the ester 115 as the trans-isomer. 

TMS production involves one specific functional group (-OH, -COOH, =NH, -NH2, or -SH), which loses an activated hydrogen and is replaced by a trimethylsilyl group (Proestos et ah, 2006). To achieve silylation, some authors have used BSTFA (N,0-hA(trimethyl-silyl)trifluoroacetamide) and TMCS (trimethylchlorosilane) successfully in several matrices (e.g. aromatic plants, cranberry fixiit) (Zuo et ah, 2002 Proestos et ah, 2006). Using silylated derivatives is advantageous for several reasons phenols and carboxylic acids are prone to silylation, these compounds can be derivatized in the same part of the process, and the minor products do not impede analysis and are well documented (Little, 1999 Stalikas, 2008). A two-step methylation procedure was used to analyze catechins and tannins in plant extracts. The first step used trimethylsilyl diazomethane (TMS-diazomethane) to pre-methylate the sample, and the second step used thermally assisted hydrolysis and methylation (THM). The pre-methylation step with TMS-diazomethane stabilized the dimer molecule m/z 540) by minimizing isomerization and reducing reactivity. (Shadkami et ah, 2009). 

Alkylation of 3-methyl-4-phenyltriazolin-5-one (70) with dimethyl sulfate (Scheme 23) affords not only the neutral 1-methyl derivative (71) but also the mesoionic compound (72) (66AC(R)i9o). On the other hand the isomeric l-methyI-5-phenyltriazolin-3-one (73) affords the mesoionic compound (74) with methyl iodide but the methoxytriazole (75) with diazomethane (76Cpb1336). 

The metabolic and/or hydrolytic products of parathion encountered as residues in the urine include both diethyl phosphoric acid and diethyl phosphorothioic acid, most probably as their salts (potassium or sodium). Derivatization of these residues with diazomethane would result in the formation of three trialkyl phosphate compounds, namely, 0,0-diethyl O-methyl phosphate (DEMMP), 0,0-diethyl 0-methyl phosphoro-thionate (DEMMTP), and 0,0-diethyl S-methyl phosphorothiolate (DEMMPTh). Earlier (15), it had been shown by combined gas chromatography-mass spectrometry and other analytical data that a later-eluting major product ca. 85%) of the methylation of diethyl phosphorothioic acid formed under the conditions of the analytical method was DEMMPTh, and the minor product formed (ca. 15%) was DEMMTP. Accordingly, all three trialkyl phosphates were observed and confirmed by mass spectrometry in the analysis of the human urine extract. Sufficient internal bond energy differences are associated with the isomeric structures DEMMPTh and DEMMTP that qualitatively and quantitatively dissimilar fragmentation patterns are observed for both isomers as can be seen from the mass spectra of these compounds shown in Figure 4. 

Theoretical predictions on photochemical and thermal isomerization of diazirines may explain numerous experimental values. Due to low and reversible relative stability of diazirines and diazomethanes, which depend on substituents (Figures 1 and 2), the spontaneous <63TL1405>, photochemical <64JA292>, or thermal <77JCS(P2)1214> isomerization of diazirines into diazoalkane has been observed, as well as reversible isomerization of diazocarbonyl compounds and corresponding diazirines. Interconversions of diazirines and diazo compounds have been considered in detail [Pg.352]

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