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3.4. Synthesis of N-F-containing compounds. N-Derivative of bis-(trifluorometansulfonyl)imide is an effective fluorinating agent for aromatic compounds [132]. The reviews regarding synthesis of compounds, containing N-F bonds, and their use in organic synthesis you can find in [133,134]. During fluorination of N-alkylsulfonamides in the CFCl3 -CHCl3 system using fluorine [135] , CH3OF[136] or CF3OF[137,138] the corresponding N-fluoroderivatives are obtained.
The fluorination of sodium salt of N-tret-butyl-p-toluenesulfonamide by cesium fluoro-oxy-sulfate in acetonitrile at 0-5oC give the N-fluoro-N-tret-butyl-p-toluenesulfonamide with high yield (69%) [139]. The fluorination of this substrate using elemental fluorine produces product only with the 14% yield [135]. It is better to fluorinate sulfonamide derivatives in the form of corresponding salts. Thus, the fluorination of sodium salt of perfluoro N-(4-pyridyl)methanesulfoamide using elemental fluorine results in formation of N-fluoro-N-(4-pyridyl)methanesulfoamide [91,140].
The derivatives of sulfonamides having perfluoroquinolyl-, perfluoro-iso-quinolyl- substituents [137] are put into reaction. The controlled fluorination of aromatic compounds using N-fluorolactams and N-fluorosulfonamides can be used for obtaining of a number of aromatic fluoroderivatives. The fluoridation of organic compounds using N-fluorosulfonamides is described by many examples [136,140]. Thus, sulfonamides of 9 type fluorinate salts of malonic acid derivatives and aromatic compounds [135,140-146].
Obtaining methods of N-fluorodialkyl(aryl)sulfonimides are based on fluorination [F2/Ar (1-3%) or XeF2] of corresponding dialkyl(aryl)sulfonimides. Base products are obtained with the yield up to 70% [137]. N-fluorosulfonimides (CF3SO2)mNFRn(SO2R')p (where m=1,2; n,p= 0,1; R' - perfluoroalkyl, -cycloalkyl, -aryl) and CF3SO2NF(SO2)aR (a=0,1) are obtained using fluorination of corresponding imides by elemental fluorine at -20oC [140-146]. Thus at F2 influence on (CF3SO2)2NH at -20oC (CF3SO2)2NF is formed with the yield 94,6% [140]. The synthesis of N-fluorosulfonimides using method is described in many works [147-149]. In the article [140] it is offered to use not amides of acids, but their lithium derivatives. Authors used diluted elemental fluorine in non-polar solvents ( ÑÍÑl3, CFCl3, HF, fluorocarbon, MeCN) at 80-135oC in presence of solid phase (NaF, CaF2) [140]. N-fluorodiphenylsulfonimide was obtained during fluorination of diphenylsulfonimide by fluorine (diluted nitrogen) in presence of sodium fluoride in acetonitrile at -40oÑ [150].
N-fluorodiphenylsulfonimide is a white crystal substance, dissoluble in plenty of organic solvents (ether, THF, CH2Cl2, MeCN, C6H5CH3), convenient in handling, non hydroscopic and stable for storage. N-fluorodimethylsulfonimide, another N-fluorodialkylsulfonimides [(CH3(CH2)nSO2)2NF, n = 1-3] and N-fluoro-[1,3,2]-dithiazine-1,1,3,3-tetraoxide was produced similarly[151]. Water or water mixture with organic solvent can be used as media. Best results are achieved with sodium salts of corresponding sulfonamides [152]. Thus, N-fluorodimethylsulfonimide is obtained at action of elemental fluorine (F2/N2 = 1:9) in acetonitrile in presence of sodium fluoride at -40oC with the yield 90% [153].
At fluorination of sodium saccharin salt by caesium fluoro-oxy-sulfate in acetonitrile at 0-5oÑ N-fluorosaccharin is obtained with the yield of 69%, while fluorine influence on this compound in methyl alcohol at -60 - -70oC results in uncovering of heterocycle and formation of o-fluorosulfonylmethylbenzoate (yield 28%) [154].
Fluorine-containing analogue of saccharine 10 is obtained by influence of diluted fluorine on sodium salt of benz-1,2,3-oxathiazine-4(3H)-one-2.2-dioxide in acetonitrile at low temperature in presence of sodium fluoride [155,156]. This reagent 10 is a crystal substance of sufficient stability and has a high capability for fluorination. Mainly it is used for fluorination of different salts, steroids and aromatic compounds.
The most active agent among N-fluorosulfonimides is N-fluoro-bis-(trifluoromethanesulfonyl)amide, obtained according the above scheme with total yield 76% . This compound has a boiling point 90-91oC and is thermally stable, it can be kept in glass and is rather effective agent for fluorination with wide field of application [147-149].
Marked with isotope 18F N-fluoro-bis-(trifluoromethanesulfonyl)amide is obtained according to the same scheme (radiochemical yield 45%) [157]. Stable white crystal powder of N-fluoro-o-benzenedisulfonimide 11 [158-160] is obtained by action of fluorine diluted by nitrogen upon î-o-benzenedisulfonimide at low temperatures.
N-F-containing compounds reveal high activity as fluorinating agents [161]. |
