N,N,N¢, or trichloromelamine (TCM) were used as effective oxidizing agents for the oxidation of urazoles and bisurazoles to their corresponding triazolinediones under mild and heterogeneous conditions at room temperature with excellent yields.

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N-Nitrosation chemistry of amines is an important and well-established reaction in organic synthesis. 1 The most general reagent is nitrous acid, generated from sodium nitrite and mineral acid in water or in mixed alchoholwater solvents. 2 Other nitrosating agents, such as Fremy's salt, 3 bis(triphenylphosphine)nitrogen(1+) nitrite, 4 N-haloamides and sodium nitrite under phase-transfer conditions, 5 oxyhyponitrite, 6 dinitrogen tetroxide, 7 solid acids (i.e., oxalic acid dihydrate, 8 inorganic acidic salts 9 and hydrolyzable chloride salts 10 ), and sodium nitrite have also been used. We were interested to find a completely homogeneous reagent for the N-nitrosation of secondary amines, and thus we have investigated a number of different reaction conditions based upon the in situ generation of NO + . In continuing of our studies on the application of NOX, 11 N 2 O 4 , 12 metal nitrate dinitrogen tetroxide complexes. 13 and complexation of transition metals with macrocyclic ethers, 14 we found that 18-Crown-6 gives an ionic complex with N 2 O 4 gas as [NO + ‚Crown‚H(NO 3 ) 2 -] in quantitative yields. In this communication we now report a simple and convenient method using this new reagent for the effective Nnitrosation of secondary amines (1) to their corresponding N-nitroso derivatives (2) under mild conditions. Different types of secondary amines (1) were subjected to the nitrosation reaction in the presence of [NO + ‚Crown‚H(NO 3 ) 2 -] (I) and dry SiO 2 in dichloromethane. The nitrosation reactions were performed under mild conditions at room temperature and take place with quantitative yields (Scheme 1).This present nitrosation reaction can be readily carried out by placing the complex [NO + ‚Crown‚H(NO 3 ) 2 -] (I), amine (1), dry SiO 2 and CH 2 Cl 2 as the solvent in a reaction vessel and efficiently stirring the resulting mixture at room temperature. The reactions were completed after 5 min. The reaction mixture was filtered, and dichloromethane was also removed by water bath (40-50°C) and simple distillation. The highly pure nitrosoamines (2) were obtained by passing the residue through a pad of silica gel.A competitive reaction was performed between dicyclohexylamine (1c) and anisole. It was observed that amine nitrosation occurred exclusively, whereas anisole remained intact in the reaction mixture after 1 h. The nitrosation reaction of diphenylamine shows the chemoselectivity of the method as the N-nitrosodiphenylamine is the only product. This system thus behaves differently from some reported methods 2 so that the nitrosonium ion (NO + ) attacks the nitrogen sites of the secondary amines even where an aromatic moiety is connected directly to the nitrogen atom.Furthermore, the chiral center of L-proline (1h) also remained intact in the course of the reaction so that L-nitrosoproline (2h) was obtained quantitatively. LNitrosoproline (2h) is a precursor of mesoionic moieties in an important class of dipolar heterocyclic compounds with special properties. 15,16 Ghorbani Choghamarani, A.; Taqiannasab, A...

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