Diazopropyne

The first representative of the acetylenic derivatives, 3(5)-ethynylpyrazole, was obtained by condensation of diacetylene with diazomethane by Kuhn and Henkel (41LA279) and later by other authors (69IZV2546), and by reaction of acetylene with diazopropyne (62AG252 68LA113) (Scheme 2). 

The standard technique for obtaining alkynylpyrazoles consists of mixing up the ether solutions of diazoalkane and diacetylene or its derivatives (or diazopropyne and acetylene) and keeping the reaction mixture either for several hours or for three weeks within a narrow temperature range (0-20°C) (Tables II and III). 

Diazopropyne reacts similarly with a monosubstituted acetylene to form 3(5)-alkynylpyrazoles (68LA113). Thus, the reaction of diazopropyne with acetylene-carboxylic acid methyl ether results in 5-ethynyl-l//-pyrazole-3-carboxylic acid methyl ether in 48 h in 62% yield. 5-Ethynyl-l//-pyrazole-3,4-dicarboxylic acid dimethyl ester was prepared by reaction of diazopropyne with acetylenedicar-boxylic acid methyl ether (Scheme 10). 

In 1972 a matrix-isolation study on the photolysis of diazopropyne (38) and some IR bands of propargylene (36) were reported in a doctoral thesis.65 In 1974, 36 was identified as one of the products of the vacuum UV irradiation of matrix-isolated propyne and allene.66... 

In the laboratory 254 has inter alia been obtained in an argon matrix by irradiation of diazopropyne (253) at 10 K [106], Matrix isolation ESR and IR studies and ab initio calculations show it to be a 1,3-diradical with C2 symmetry, as indicated in Scheme 5.39 [107]. Irradiation with shorter wavelength light induces a 1,3-hydrogen shift by which the triplet propynylidene 254 is converted into the singlet propadienyli-dene 255, the parent system of unsaturated carbenes such as 251 (Scheme 5.39) [108]. 

Other novel diazo compounds that have been subjected to 1,3-dipolar cycloaddition with activated alkenes, and that give unusually functionalized pyrazolines (Scheme 8.7), include l-diazo-3-trimethylsilylpropan-2-one (20) (49), 2-diazo-methyl-4(57/)-furanones (21) (50), methyl 2-diazo-5-methylanilino-5-oxopentano-ate (22) (51), 2-(acylamino)-2-diazoacetates (23) (51), ethyl 2-diazo-4,4,4-trichloro-3-(ethoxycarbonylamino)butyrate (24) (52), and diazopropyne (53). 

Similar ra-selective [2 + 1] cycloadditions are described for 1-chloroethenylcarbene, 2,3-dichloroethenylcarbene, and trichloroethenylcarbene, which are generated from the corresponding diazo compounds (see Vol. E 19b, pp 687-690)3. cis- and tra/w-l-Ethynyl-2-(trimethylsilyloxy)cyclopropane are available by rhodium(II) acetate catalyzed addition of diazopropyne to (trimethylsilyloxy)ethene again this reaction exhibits good cis selectivity4. 

Skell and Klebe reported in 1960 that photolysis of diazopropyne 65 in E- and Z-2-butene (Scheme 17) gives a carbene that is slightly nonstereospecific and a mixture of three cyclopropanes (67,68, and 69) in the ratios of 4 2.5 1, respectively, with Z-2-butene being isolated. ... 

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