Diazomethanes, thermolysis

The simplest carbene is the compound called methylene ( CH2)- Methylene can be prepared by the decomposition of diazomethane (CH2N2), a very poisonous yellow gas. This decomposition can be accomplished by heating diazomethane (thermolysis) or by irradiating it with light of a wavelength that it can absorb (photolysis) ... 

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),... 

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 ). 

The first carbene ever isolated was la, which was prepared using the most classical route to transient carbenes, namely, the decomposition of diazo compounds. The [bis(diisopropylamino)phosphino](trimethylsilyl)diazomethane precursor (la) was obtained by treatment of the lithium salt of trimethylsilyldiazomethane with 1 equiv of bis(diisopropylamino)chlorophosphine. Dinitrogen elimination occurs by photolysis (300 nm) or thermolysis (250 °C under vacuum) affording carbene la as a red oily material in 80% yield (Scheme 8.1). Carbene la is stable for weeks at room temperature and can even be purified by flash distillation under vacuum (10-2 Torr) at 75-80 °C. 

The structure assignment of the diazomethane products as 4-substituted thiatriazolines (16) is based on their thermolysis. On heating in toluene at 120-130° for several hours, this type of compound loses nitrogen with formation of benzothiazoles29 [Eq. (19)] in contrast to ordinary 5-aminothiatriazoles, which yield cyanamides, sulfur, and nitrogen. 

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>. 

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