Pentyl nitrite nitration with

To date, there has been no report of the nitrosation of imidazole itself. There are, however, a number of examples of nitrosation of substituted imidazoles in basic medium. The observation that such reactions do not occur with Af-substituted imidazoles implicates the imidazole anion as the likely substrate. Substitution generally occurs at C-4 or C-5 and may be accompanied by some nitration. In the presence of sodium ethoxide, pentyl nitrite nitrosates 4-phenyl-, 2-methyl-5-phenyl- and 2,5-diphenyl-imidazoles at the vacant 4- or 5-positions. The reaction apparently failed with 5-methyl-2-phenyl- and 4,5-diphenyl-imidazoles (58G463). 

Acid catalysis is preferable to base for the condensation of 5a-cholestan-3-one (341) with pentyl nitrite to form the hydroxyimino-ketone (342). The dioxime (343) afforded the [2,3-c]furazan 2-oxide (344) on oxidation with hypochlorite. Nitration of the 3-ketone (341) with ethyl nitrate and base gave the 2-nitro-enol (345) the derived 3-oxime (346) gave the furazan oxide (344) on reaction with acid. Nitration of 5a-cholestan-7-one gave the 6a- and 6)5-nitro-ketones (347), apparently the first epimeric pair of steroidal nitro-ketones to be... 

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