Pyrazolines from diazoalkanes

Cycloaddition of diazoalkanes to 6-6 bonds was among the first reactions tested on the carbon cages41 and affords isolable fullerene-fused pyrazolines as primary adducts. Photochemically induced extrusion of N2 from the latter yields 6-6-closed methanofullerenes having the functionalized bond embedded in a cyclopropane substructure, whereas the thermal process affords 6-5 open homofullerenes in which a methylene group is bridging the open junction between a six- and a five-membered ring.15-17... 

The nitrogen extrusion from 1-pyrazolines and 3H-pyrazoles giving cyclopropanes and cyclopropenes, respectively, has been extensively reviewed The cyclopropane synthesis from 1-pyrazolines can be executed thermally as well as photochemically, but the latter method generally gives substantially better results than the former. The major side reaction observed in the thermal process is the production of olefins, which arise in the migration of a substituent from the C(4) to C(3) position. A retro-1,3-dipolar addition producing a diazoalkane and an olefin has been observed in certain cases. The decomposition of 3-acyl- or 3-alkoxycarbonyl-1-pyrazolines is catalyzed by acids, such as perchloric acid and boron trifluoride and by Ce The stereochemical course... 

Di, tri-, and tetrahalocyclopropenes undergo cycloaddition with diazoalkanes to give unstable pyrazolines, which readily rearrange to pyridazines with loss of hydrogen halide. Tetrachlorocyclopropene is commercially available but many of the bromo compounds are easily prepared in two steps from vinyl bromides by addition of dibromocarbene, followed by reaction with methyllithium, the last step being carried out in situ for the cycloaddition step. ... 

The dienophilicity of thiet 1,1-dioxide was utilized to synthesize (73) from tetracyclone, whilst it acted also as a good dipolarophile towards diazoalkanes, giving mixtures of 1-pyrazoline derivatives (74) and (75) in which the isomers (74) predominated, except in the cases of diazomethane and diazoethane, where (75) was the major isomer. Ethyl diazoacetate on the other hand gave the 2-pyrazoline (76). These compounds arc potentially useful for the synthesis of bicyclobutanes by sequential expulsion of nitrogen and sulphur, and thermolysis or photol3rsis of (74 = R =... 

The reaction of diazomethane with a,p-xmsaturated carbonyl compounds under classical protic conditions has been shown to produce pyrazoline products arising from 1,3-dipolar cycloaddition [3, 4]. Limited examples of a,p-xmsaturated carbonyl substrates undergoing ring expansion in the presence of Lewis acid promoters have been reported. It was not until the introduction of Lewis acids for diazoalkane ring expansion that these types of substrates were even reactive. In Drege s... 

Thermal extrusion of dinitrogen from the adduct of benzene with diazomethane, and from the pyrazoline adducts of fullerenes with diazoalkanes (to give 6-5-open methanofullerenes), are believed to feature a Mobius aromatic transition state with a highly anisotropic magnetic susceptibility. ... 

A variety of substituted diazoalkanes have been examined. Rodina et reported formation of a spiro pyrazoline 31 from the cyclic diazoketone 30. The product on further heating to 141°C loses 1 mole of N2 to yield a spiro cyclopropane derivative 32. 

Formation of esters by reaction of diazoalkanes with carboxylic acids is a mild and often quantitative procedure. It is particularly useful for the preparation of methyl and ethyl [4], benzyl [3, 58], and benzhydryl esters [45, 59, 60], although not on a large scale. The reaction is initiated by proton transfer from the carboxyl group and 0-alkylation is a competing reaction with phenolic acids. Diazoalkanes may also add to carbonyl [61] and olefinic linkages [62]. Thus the shikimic acid derivative (16) with a limited amount of diazomethane at low temperature gives the methyl ester (17) but with an excess of the reagent forms the isomeric pyrazolines (18 and 19) [63, 64]. 

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