2- Benzyl-3-methyl-pyrazole 1 -oxide

The isomeric 2-benzyl-3-methyl-pyrazole 1-oxide 193 reacts similarly to give the 3-iodomethyl-pyrazole 196. In this case, the 3-trimethylsilyloxy-methyl compound 197 is formed as a by-product. Most likely, the sily-loxymethyl compound 197 arises when the liberated silyloxyanion acts as a nucleophile replacing the silyloxy group in a regenerative fashion. The silyloxy compound 197 is readily hydrolyzed to hydroxymethyl-pyrazole 198. The 3-methyl-pyrazole 1-oxide 193 reacts five times faster than the 5-methyl isomer 189 as shown by a competition experiment (1992JCS(P1)2555). The iodomethyl-pyrazoles 192 and 196 are versatile starting materials for further transformations in the pyrazole side chain (Scheme 55). 

The lateral protons of the isomeric 4-methyl-pyrazole 1-oxide 199 are not activated, since lateral deprotonation does not give rise to a neutral species. Under similar conditions the 4-methyl isomer 199 reacts at the 3-position producing l-benzyl-3-iodo-4-methyl-pyrazole 202 and... 

In some cases l-methyl-5-nitro- and l-methyl-3,5-dinitropyrazole can form as a result of deoxygenation [76], Nevetheless, the nitration of 2-benzylpyrazole 1-oxide by sulfuric-nitric acid mixture leads to 2-benzyl-3-nitropyrazole 1-oxide in quantitative yield. Further nitration takes place in the phenyl 4-position forming 3-nitro-2-(4-nitrobenzyl)pyrazole 1-oxide and then in the pyrazole 5-position to give 3,5-dinitro-2-(4-nitrobenzyl)pyrazole 1-oxide as the final product [77],... 

Benzyl-3-methyl-1 H-pyrazol-2-oxid wird mit Trimethyloxoniumtetrafluoroborat (2 h Nitro-methan) am N-Oxid-O-Atom zu l-Benzyl-2-methoxy-3-methyl-pyrazoliumtetrafluoroborat me-thyliert (80% Schmp. 107-109°). Mit 2,2-Dimethyl-propansaure-chlorid und Silbertrifluor-... 

Bei der Bromierung von l-Benzyl-3-(carboxy-methoxy)-4-methyl-lH-pyrazol in waBriger al-kalischer Losung kommt es neben der Bromierung in 4-Position zur Oxidation in 5-Position2330. 

The pyrazofurin analogue 98 has been prepared by a sequence involving cycloaddidon of an alkyne to (2,3,5-tri-0-benzyl-p-D-ribofuranosyl)diazomethane,i ii whilst 99 was made by oxidation of a protected ribosyl p-nitrophenylhydrazone and cycloaddidon of the resultant nitrilimine widi methyl propiolate.1 Skmie 3- and 4-D l rxofiitaiiosyl pyrazoles have been prq red acid-catalysed cyclizad[Pg.258]

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