Pentyl nitrite nitrosation 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). 

Typical nitrosating agents are sodium nitrite with mineral acids or pentyl nitrite with mineral acids. A relatively new reagent, nitrosylsulfuric acid, has been used to nitrosate primary aromatic amines. 

Tertiary aromatic amines have also been nitrosated with pentyl nitrite in hydrochloric acid [21a],... 

Diazotization in organic solvents allows solid diazonium salts to be isolated. Diazotization can be carried out using an ester of nitrous acid, such as pentyl nitrite, in a solvent such as acetic acid or methanol. A procedure has also been described for isolating diazonium tetrafluoroborates, in excellent yield, by carrying out the diazotization with boron trifluoride etherate and f-butyl nitrite in ether or dichlorometh-ane at low temperature. Another method for the preparation of a variety of diazonium salts in a nonaqueous medium makes use of the chemistry of bis(trimethylsilyl)amines (8). These compounds react in dichloromethane with nitrosyl chloride and other nitrosating agents which are generated in situ. Thus, benzenediazonium chloride was isolated (96%) from bis(trimethylsilyl)aniline. 

R = (PhNH)2P(0), R = H) was resolved through the use of a D-mannose ethylorthoacetate derivative. Further phosphorylation provided (19 R = R = (PhNH)2P(0) ) from which the anilino groups were removed by nitrosation with pentyl nitrite, and the benzyl groups in the usual manner, to give laevorotatory... 

As the proton release is often too slow under the acidic conditions used for the diazotization of aromatic amines, syntheses of aliphatic diazo compounds by this method are carried out without an excess of mineral acid. Usually, equimolar amounts of amine, HCl and NaN02, or amine and NOCl, are used. A better alternative is nitrosation with pentyl nitrite in the presence of up to 30% acetic acid, as found by Takamura et al. (1975). Yields higher than 60% were obtained with a-amino-substituted esters of some aliphatic carboxylic acids. 

Thebaine-maleimide adducts have been prepared, and the Diels-Alder reaction of thebaine with cyclic azo-dienophiles has been investigated. " Nitrosation of thebaine hydrochloride with nitrosyl chloride or pentyl nitrite in methanol or ethanol gives 7-hydroxyiminoneopinone dimethyl or diethyl acetal. " The chemistry of 14-bromocodeinone and its dimethyl acetal has been studied in some detail, including catalytic hydrogenation, "" methanoly-sis, " debromination, "" dehydrobromination, " and solvolysis.Efforts are continuing in the preparation of novel analgesics in the morphine-thebaine series. 

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