3(5)-Nitropyrazoles, such as 3,5-dmitropyrazole (2f), can be readily synthesized by thermal rearrangement of A-nitropyrazoles. In turn, 3 (5 ),4-dinitropyrazoles are obtained by further nitration of some 3(5)-nitropyrazoles.The direct nitration of pyrazole, using nitric acid or mixtures of nitric acid and sulfuric acid,4,5 leads to substitution in the 4 position, in line with the behavior of other electrophilic reagents. Moreover, no further nitration of 4-nitropyrazoles has been reported in the literature. Reports on formation of 3-nitropyrazoIes either concern compounds synthesized by other methods such as ring closure reactions4,6 or by nitration of 1,4disubstituted pyrazo!es,7,8a,b neither of which appear to be general methods for the synthesis of 3-nitropyrazoles. It is worth notice that in the latter case further nitration to 3,5-dinitropyrazoles can occur.7 Recently three different groups of workers independently reported on the synthesis of the unsubstituted 3(5)-nitropyrazole (2a). Bagal, et al.,e obtained 2a via diazotation of 3(5)-aminopyrazole, and Birkofer10 substituted the trimethylsilyl group in 3(5)-trimethylsilylpyrazole by a nitroso group, which
The use of the tertiary base 1,4‐diazabicyclo[2,2,2]octane, together with 1‐fluoro‐2,4‐dinitrobenzene in the solvent DMF, proved to be an efficient method for the introduction of the 2,4‐dinitrophenyl (DNP) group at different positions, including the anomeric centre of glucose and galactose. The introduction of the DNP ethers at the anomeric centre leads exclusively to the formation of β‐DNP ethers. The latter derivatives can be easily converted with potassium carbonate in DMF into the α‐DNP ethers. The X‐ray analysis of 2,4‐dinitrophenyl‐2,3,4,6‐tetra‐O‐acetyl‐α‐D‐gluco‐pyranoside is discussed. The DNP group can also be used as a protective group in the synthesis of a disaccharide (i.e. 8) and as a UV probe to monitor (254 nm) and analyse (HPLC) sugar intermediates.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.