Thermolysis of Diazomethane

The fragmentation of diazomethane to methylene and dinitrogen has been dealt with computationally in considerable detail [27]. The computed potential curves displayed in Fig. 9.3 show that which is an excited triplet at the equi- 

The correspondence diagram in Fig. 9.4 can be applied to either the selective production of HDH2(i4i) or H2(Bi) or to the simultaneous formation of both. The ground-state configuration of the valence electrons of N2 (Section 3.2.2), desymmetrized from Dqo/i to with the aid of Table 3.2, can be condensed to  

In order to produce the closed shell singlet, the molecule has to bend in the zx plane, as shown in (a) of Fig. 9.5, so the N2 fragment departs at an angle to the molecular axis. In order to form the triplet, one electron from the uppermost singlet geminal (61) of the reactant moves to an orbital of CH2 with the same irrep the other is obliged to go to the totally symmetric a orbital of methylene. 

The flatter the curve the greater the density of vibrational states. 

The reader who deplores pictorializations of this kind can be reassured by the fact that the formal requirements of spin-orbit coupling are fulfilled. 

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Thermolysis The thermolysis of diazomethane was studied by Staudinger 2) a long time ago. In the presence of CO some ketene was formed most probably by the reaction between methylene and CO. 

Kinetic studies of the thermolysis of diazomethane were carried out by various authors. These experiments demonstrated that the decomposition of diazomethane was a first order reaction 41-43) Similar investigations of the p5n olysis of diphenyl-diazomethane in xylene or 1-methylnaphthalene also showed that the disappearance of diphenyl-diazomethane is a first order process. It may be concluded that a free carbene is involved in these reactions, in accordance with the following scheme ). 

Figure9.4. Correspondence diagram for thermolysis of Diazomethane (from Fig. 2 of reference [14])...

Intramolecular attack of the carbenes shown in Scheme 30a provides benzo[6]cyclo-hepta[(5 ]-furans and -thiophenes, but the nitrogen analogue (X = NH) yields 9,10-dihydro-acridine 81AJC1037). Photolysis of 2-biphenyl isocyanide (Scheme 30b) (72JOC3571) and thermolysis of 2-biphenylsulfonyl diazomethane (Scheme 30c) (72CC893) also result in ring expansion. 

Reaction of lithiated silyl- and diaminophosphino-diazomethanes (30, R = Me3Si, (R 2N)2P) with triphosphenium salt, [((Me2N)3P)2P]+BPh4 to give the respectively substituted [l,2,4]diazaphospholes has also been described to take place via the corresponding phosphaalkynes. Triphosphino substituted [l,2,4]diazaphosphole has been obtained by thermolysis of the phosphino-phosphiranyl-diazomethane via the... 

The photocycloaddition of an excess of cyclobutenecarboxylic acid (380) and (—)-piperitone (381), followed by esterification with diazomethane, gave the adduct (382). Reduction of (382) afforded the lactone (383). Upon thermolysis in decane at 174 °C, the lactone (383) was converted to the dihydroisoaristolactone (384). Thermolysis of (382) in refluxing decane gave quantitative yield of the compound... 

The photolysis or thermolysis of diazo compounds results in the formation of carbenes. These reactions were identified as early as 1901 by Hantzsch and Lehmann D and Staudinger and Kupfer who decomposed diazomethane photochemically and thermally, respectively. The subsequent work of Hine 3) and Doering ) started the era of carbene chemistry. Excellent reviews of the chemistry of carbenes are available 5-27),... 

Diazomethane and its simple analogs undergo cycloaddition to unsaturated compounds both directly and after conversion to carbenes. The direct cycloadditions are 1,3-dipolar for the most part and provide access to pyrazolines and pyrazoles. Intramolecular cyclizations were recognized as early as 1965 95 The two main methods used in generation of diazo compounds for subsequent intramolecular cycloaddition include thermolysis of tosylhydrazone salts and thermolysis of iminoaziridines. Decomposition of nitros-amines has also been employed. 

The diazoacetonitrile-imine reaction may be considered complimentary to azide addition to cinnamonitriles because in the latter case only triazoline thermolysis products result.284 The reversed order of reactivity of the diazoacetonitrile to that of diazomethane implies an electrophilic attack on the imine and is explained in terms of a LUMOdi MC lonit[ile-HOMOin,int controlled interaction. Thus electron-rich enamines, which do not react with diazoalkanes, may be expected to react with electron-poor diazo compounds. 

C6o reacts with diazomethane to yield fulleroids [97,99,100,234], Carbene generated from the thermolysis of precursors such as diazirines, sodium trichloroac-etate, cyclopropene, oxadiazole, and tosylhydrazone [60,235] adds onto C6o leading to methanofullerenes [12,15,236], Recently, Akasaka et al. described the photochemical reaction of diazirine with C6o [237], Irradiation of a benzene solution of 2-adamantane-2,3 -[3H]-diazirine 58 and C6o with a high pressure mercury lamp (cutoff <300 nm) at 15°C in a Pyrex tube resulted in the formation of mixture of the isomers 59a and 59b in a ratio of 51/49 (Scheme 24). 

Partially and perfluorinated thioketones and thioaldehyde were stabilized as anthracene adducts (70). The adducts (70) were prepared in moderate yield from the corresponding carbonyl compounds with P4S10 or Lawesson s reagent in the presence of anthracene under toluene reflux. The generated thiocarbonyl compounds are not accessible in bulk due to their tendency towards polymerization. By thermolysis of the anthracene adducts (70) in the presence of C,N-bis(triisopropylsilyl)nitrilimine (NI), 1,3,4-thiadiazole derivatives (71) were obtained. Also, 1,3-dipolar cycloaddition with bis(trimethylstannyl)diazomethane (BTSD) to give consecutive products (72) from a 1,2-metallotropic migration of primary adducts was discussed. [95LA95]... 

The perfluorinated cyclopropenes (292, X = C(CF3)NH) may be prepared from (293) by 1,3-dipolar addition of diazomethane followed by desulphurisation with, triphenylphosphine to produce, (294), and then thermolysis. Addition of (292, X = C(CF3)0) to 2,3-dimethylbutadiene occurs predominantly in an endo-manner, the intermediate undergoing an intramolecular ene-reaction to produce (295). In the same way reaction with pyrrole leads to (296), in this case presumably by an intramolecular nucleophilic attack in the initially formed endo-adduct 237). 

Intramolecular attack of the carbenes 32 provides benzo[7]cyclohepta[<7] furans and thiophenes 33 (Scheme 15). Photolysis of 2-biphenyl isocyanide 34 (Scheme 16) <1972JOC3571> and thermolysis of 2-biphenylsulfonyl diazomethane 35 (Scheme 17) <1972CC893> also result in the formation of ring expanded products. 

The thermolysis of bis(trialkylstannyl)diazomethane 29 affords bis(trialkylstannyl)carbo-diimides 30 in good yields. ... 

Reaction of thioketones 317 with an excess of diazomethane 318 gave 2,5-dihydro-l,3,4-thiadiazoles 319. Thermolysis of 319 in refluxing benzene for 2h gave thiocarbonyl 3 -methylides 320, which underwent electro-cyclization to give corresponding thiiranes 321 (Scheme 92) <2005EJ01519>. 

Double addition of diazomethane to cinnamylidene cyanoacetic ester 50 (EWG = COOR ) and corresponding dinitriles (51) (EWG = CN) followed by thermolysis gave rise to pyrazoline-substituted cyclopropanes (52) which upon photolysis and acid treatment afforded biscyclopropanes (53) and tricyclic compounds (54) respectively. ... 

Thermolysis of pyrazolines was also used for aminocyclopropane synthesis. The corresponding starting materials were obtained from diazomethane and an alkene bearing a suitable nitrogen functional group, e.g. an amido or azido moiety. 

Triarylcyclopropanes 3 were synthesized in moderate to good yield by thermolysis of the corresponding diaryldiazomethanes in refluxing benzene containing styrenes. 4,5-Dihydro-3//-pyrazole derivatives were not detected in any of these reactions, but the involvement of such intermediates is indicated by kinetic studies, which gave a g value of 1.68, indicating nucleophilic addition of the diazomethanes. 

Addition of diazoalkanes to a, -unsaturated amides and nitriles, although less frequently exploited than additions to esters, proceeds in a similar manner. Hence, the addition of diazomethane to 2-methylpropenenitrile (a-methylacrylonitrile) followed by thermal deazetization gave a good yield of 1-methylcyclopropanecarbonitrile (Houben-Weyl, Vol. 4/3, p 48). Similar problems with alkene formation are encountered to those noted in the ester series for example, in the thermolysis of 3,3-dicyano-4-isopropyl-4,5-dihydro-3/f-pyrazole 21, prepared from 20 by the addition of diazomethane. In this case, however, not only does the addition of copper(II) chloride accelerate the elimination of nitrogen, but it also reverses the product ratio in favor of the cyclopropane 23. " ... 

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