Pyrazoles deuterium-labelled

Reactions of Pyrazoles. A -Nitropyrazoles nitrate aromatic compounds under L wis acid conditions. Pyrazole as a nucleophile undergoes two successive cine-substitutions with 1,4-dinitropyrazole, yielding the terpyrazolyl (256). Irradiation of the deuterium-labelled cyanopyrazole (257) affords a mixture of the isomeric imidazoles shown in Scheme 5. ... 

Pavlik and Kurzweil further studied the phototransposition chemistry of 1-methylpyrazoles in which the various ring carbon atoms are systematically labeled with a second methyl group. The primary products shown in Table 2 and the results of deuterium labeling studies shown in Table 3 confirm that these dimethylpyrazoles undergo only pyrazole to imidazole phototransposition by as many as three distinct permutation pathways. Thus, whereas 1,5-dimethyl-pyrazole 16 transposes by the P4, Pg. and P7 pathways to yield a mixture of 1,5-, 1,2-, and 1,4-dimethylimidazoles 19, 17, and 18 respectively, 1,3-dimethylpyrazole 14 transposes only via the P4 and Pg pathways to form 1,2-and 1,4-dimethylimidazoles 17 and 18. Finally, 1,4-dimethylpyrazole 15 trans-... 

Protonation of 992 occurs at a pyrazole group reductive elimination of methane occurs during this reaction and the square-planar species thus formed can be isolated as a complex with MeCN as a ligand (1003, Equation (187)). Deuterium labeling experiments indicate the presence of the intermediate with methane as a ligand. 

The photochemistry of 1-methylpyrazoles 12 through 14, in which the various ring carbons are systematically labeled with a second methyl group, has also been studied. The primary products shown in Scheme 8, and the results of deuterium labeling studies shown in Scheme 9 confirm that these dimethyl-pyrazoles undergo only pyrazole-to-imidazole phototransposition by as many as three distinct pathways. 

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