Nitrosonium fluoroborate

It has been reported that 1-hydroxyimidazoles (rather than imidazoles [28]) are accessible in high yields from reaction of nitrosonium fluoroborate with acetonitrile and the appropriate alkene titanium(III) chloride reduces the hydroxyl function [24]. 

Both nitronium and nitrosonium salts are effective initiators but with quite different results. Thus, propene and nitronium fluoroborate react to produce the secondary a-nitrocarbenium ion which undergoes Ritter reaction with acetonitrile to yield amide (118). Under similar conditions, nitrosonium fluoroborate leads to heterocyclic products. Intramolecular reaction of the nitroso and nitrilium groups, followed by prototropic shifts, affords the iV-hydroxy imidazolium salt (119). This may be either neutralized to produce the iV-oxide or reduced to the imidazole (120 Scheme SS). 

These reactions are typified by Bredereck s formamide synthesis . This has been applied to the synthesis of 4,5-dimethylimidazole (as its formic acid complex) from acetoin and formamide <91JHC1819>. A similar reaction leads to 5-methylhistamine (243) <8lJHC83l>. 1-Hydroxyimidazoles are accessible in high yield from reaction of nitrosonium fluoroborate with acetonitrile and appropriate alkenes (Scheme 177) <84TL1319>. 

Research on the fluorination of aromatic amines has provided access to 4-fluoro-2,l,3-benzo-thiadiazole (77). Treatment of 4-amino-2,l,3-benzothiadiazole (1) with nitrosonium tetra-fluoroborate (NOBF4), followed by heating of the resulting diazonium salt, gave the aryl fluoride (77) in 23% yield <92SC73>. 

Nitrosonium tetrafluoroborate reacts with alkyl sulfilimines (R-N = S = 0) to give alkyl fluoroborates, which are probably precursors of alkyl fluorides, since no water is produced. No further details were reported.190... 

Electrochemical oxidation of 1,3-ditellurole leads to its stable radical cation 59 ( max = 560 nm), which is also formed when nitrosonium tetra-fluoroborate in CH2C12 is employed as an oxidant (85JA6298). Treatment with hydrazine hydrate smoothly restores the initial ditellurole. Similar to the radical cation of naphthof 1,8-cd][ 1,2]ditellurole (81CB2622), 59 does not display an ESR signal and dimerizes to dication 60 (Amax = 610 nm) on lowering the temperature of the solution to -60°C. The formation of 60 is facilitated by an increase in the concentration of the 1,3-ditellurole. 

Despite the reactivity of carbazole cation-radicals, that of 9-ethylcarbazole has been trapped by nucleophiles, e.g., I", NO2,475 Thus, iodo and nitro derivatives of 9-ethylcarbazole result, along with 9,9 -diethyl-3,3 -bicarbazole, when 9-ethylcarbazole is oxidized by iodine in the presence of iodide and nitrite.473 Oxidation in the absence of nucleophiles, e.g., by nitrosonium tetrafluoroborate, permits the synthesis of the cation-radical fluoroborate salts of the 3,3 -bicarbazoles476 The reactivity of the cation-radical of 9-vinylcarbazole has been reviewed recently.11,477... 

Fluoruarenes from Anilines via the One-Pot, Thermal Balz-Schiemann Reaction Using Nitrosonium Tetra-fluoroborate General Procedure ... 

Alkylation of thioamides with Meerwein s reagent (trialkoxonium fluoroborate) proceeds via a thioiminoester and subsequent base hydrolysis with sodium carbonate (equation 32). For the synthesis of 2-pyridones from 2-thiopyridones, chloroacetic acid has been used. ° Mild reaction conditions are provided by nitrosyl species which are derived from a variety of reagents excess NaNOa/HCP in aqueous medium, nitrosonium tetrafluoroborate in dichloromethane, dinitrogen tetroxide in acetonitrile at low temperature and f-butyl thionitrate. ... 

Nitrosyl(1,4,8,11-tetrathiacyclotetradecane)rhodium(III) Tetra-FLUOROBORATE, [Rh(TTP)NO] (BF4)o. To a solution of 0.25 g [Rh(TTP)]-BF4 in 40 ml acetonitrile, a solution of 0.1 g (excess) nitrosonium tetra-fluoroborate (Aldrich) dissolved in 5 ml acetonitrile was added drop-wise. During the addition, the solution turned from the golden color of [Rh(TTP)] to a bright green. The volume of the solution was then reduced to approximately 10-15 ml, and small aliquots of diethyl ether were added for 30 min. The bright green microcrystalline product was collected, washed with diethyl ether, and dried by pumping on a vacuum line. 

Nitnosyl fluoride reacts with sulphur dioxide and the compound SO2 NOF can be isolated. It reacts with fluorides to form the respective nitrosonium fluorocomplexes, such as the fluoroborate or the fluorosilicate . ... 

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