Nitronium tetrafluoroborate, from nitric

Nitrones, reaction with olefins, 46, 130 Nitronium tetrafluoroborate, from nitric add, boron trifluoride, and hydrogen fluoride, 47, 56 in nitration of aromatic rings, 47, 60... 

The dinitrocubane 362 was prepared from the corresponding diisocyanate in this way404. In contrast, treatment of isocyanates with nitronium tetrafluoroborate and nitric acid yields A,A-dinitroalkylamines, e.g. BuN(NC>2)2 from butyl isocyanate405. N-Nitrosodialkylamines are oxidized to the corresponding nitro amines by hydrogen peroxide in aqueous acetic acid, e.g. equation 123406. 

Alkyl lV,lV-dinitramines (154) have been prepared from the reaction of the tetraalkylam-monium salts (155) of primary nitramines with nitryl fluoride in acetonitrile at subambient temperature. The same reaction with the primary nitramine or its alkali metal salts yields the corresponding nitrate ester. Treatment of the ammonium, potassium, or lithium salts of primary nitramines (156) with a solution of nitronium tetrafluoroborate in acetonitrile at subambient temperature yield alkyl iV,iV-dinitramines. ° The same reactions in ether or ester solvents enables the free nitramine to be used. The nitrolysis of A-alkylnitramides (157) and N,N-diacylamines with nitronium tetrafluoroborate in acetonitrile, and the nitration of aliphatic isocyanates with nitronium tetrafluoroborate and nitric acid in acetonitrile, also yield alkyl A,A-dinitramines (154). 

Another aspect of my early research in Budapest was in nitration chemistry, specifically the preparation of nitronium tetrafluoroborate, a stable nitronium salt. 1 was able to prepare the salt in a simple and efficient way from nitric acid, hydrogen fluoride, and boron trifluoride. 

Trinitrochlorobenzene (picryl chloride) (87) can be prepared from the nitration of 2,4-dinitrochlorobenzene with nitronium tetrafluoroborate or mixed acid composed of fuming nitric acid and oleum. Picryl chloride is also synthesized from the reaction of phosphorous oxychloride with the pyridinium salt of picric acid. ... 

Graindorge and co-workers" reported the synthesis of 2,5,7,9-tetranitro-2,5,7,9-tetraaza-bicyclo[4.3.0]nonane-8-one (113) (K-56, TNABN) from the nitration of 2,5,7,9-tetraazabi-cyclo[4.3.0]nonane-8-one dihydrochloride (112) with dinitrogen pentoxide in absolute nitric acid, the latter obtained from the condensation of urea with l,4-diformyl-2,3-dihydroxy-piperazine (111) in hydrochloric acid. Treatment of (112) with nitronium tetrafluoroborate in nitromethane results in the nitration of the piperazine ring nitrogens only and the isolation of (114) in 86 % yield (Table 5.2). 

The nitrogen atoms of heterocycles like imidazoles and triazoles have been converted into IV-nitroimide groups. The A -nitroimide (164) is synthesized from 1-amino-1,3,4-triazole (162) by IV-amination of the tertiary nitrogen with 0-picrylhydroxylamine, addition of nitric acid to give the nitrate salt (163), followed by IV-nitration with nitronium tetrafluoroborate in acetonitrile. The 1,2,3-triazole (165) and the imidazole (166) ° are synthesized in a similar way. The synthesis of IV-nitroimides has been the subject of an excellent review. ... 

The related pyrido[3,4- ]-l,2,3>4-tetrazine 2,4-dioxide 11 was accessed using a similar sequence of reactions, starting with the hydroxylamine 172 as shown in Scheme 30. The key differences are that the 4-amino derivative 175 was accessed through displacement of an ethoxy group from the intermediate 174 rather than by the chlorine displacement used above, and that ring closure this time could only be achieved with nitronium tetrafluoroborate. Nitric anhydride, in contrast to the reaction shown in Scheme 29, gave no product <2004RCB2577>. 

The results of nitration reactions depend on reagents and the acidity of the medium. Thus fuming nitric acid in concentrated sulfuric acid converts (410a) to the 3-nitro derivative while with acetyl nitrate reaction occurs exclusively at C-4 (equation 50). The nitration in the 4-position can also conveniently be done with nitronium tetrafluoroborate. The reduction of these nitro compounds by hydrazine in the presence of palladium on charcoal provides a versatile route to 4-amino-7,6-borazarothieno[3,2-c]pyridines (75ACS(B)46l>. In the nitration of 4,5-borazarothieno[2,3-c]pyridines (e.g. 409a), peri effects from the substituents on the boron atom lead to formation of a considerable amount of the 2-nitro derivatives. 

Abstract Synthesis methods of various C- and /V-nitroderivativcs of five-membered azoles - pyrazoles, imidazoles, 1,2,3-triazoles, 1,2,4-triazoles, oxazoles, oxadiazoles, isoxazoles, thiazoles, thiadiazoles, isothiazoles, selenazoles and tetrazoles - are summarized and critically discussed. The special attention focuses on the nitration reaction of azoles with nitric acid or sulfuric-nitric acid mixture, one of the main synthetic routes to nitroazoles. The nitration reactions with such nitrating agents as acetylnitrate, nitric acid/trifluoroacetic anhydride, nitrogen dioxide, nitrogen tetrox-ide, nitronium tetrafluoroborate, V-nitropicolinium tetrafluoroborate are reported. General information on the theory of electrophilic nitration of aromatic compounds is included in the chapter covering synthetic methods. The kinetics and mechanisms of nitration of five-membered azoles are considered. The nitroazole preparation from different cyclic systems or from aminoazoles or based on heterocyclization is the subject of wide speculation. The particular section is devoted to the chemistry of extraordinary class of nitroazoles - polynitroazoles. Vicarious nucleophilic substitution (VNS) reaction in nitroazoles is reviewed in detail. 

The nitronium ion (NO2), generated as indicated earlier from the action of sulfuric acid (H2SO4) on nitric acid (HONO2)(Scheme 6.83), introduced in the form of nitronium tetrafluoroborate (N02 BF4) or formed in situ from the reaction of nitric acid (HONO2) with ethanoic anhydride (acetic anhydride [(CH3CO)2]) (Equation 6.102) also reacts with napththalene (Table 6.13, example 2) to give substitution at both C-1 (C-a) and C-2 (C-P) as... 

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