HEXAFLUOROACETONE IMINE

Cycloaddition reactions where bis(trifluoromethyl)-substituted hetero-1,3-dienes act as dienophiles have been descnbed for open-chain and cyclic dienes [115, 126, 127] The balance of the diene -dienophile activity of bis(tnfluoro-methyl)-substituted hetero-l,3-dienes can be influenced strongly by the substituents bonded to the inuno nitrogen atom For instance, A/-(arylsulfonyl) denvatives of tnfluoroacetaldimine and hexafluoroacetone imine do not act as dienes but exhibit only the dienophile reactivity of electron deficient imines [5 229, 234,235, 236 237] (equation 52)... 

Sokolov and Aksinenko described a series of transformations of 2-aminoazoles and azines with A-ethoxycarbonyl-hexafluoroacetone imine <2003IZV2053>. In this research, these authors found that 2-aminothiazoline 234 can be transformed to the ring-closed compound 235 in good yield (71%). 

Caution This procedure should be carried out in a good hood and behind a shield to avoid exposure to the toxic compounds, hexafluoroacetone imine and hydrazine. 

If it is inconvenient to distill the hexafluoroacetone imine directly from a cylinder, it may be condensed first in a calibrated cold trap cooled to —10 and (hen distilled from the trap into... 

About 14 g. (17%) of hexafluoroacetone imine can be recovered during the redistillation step if the receivers for both distillations are cooled to —10° or lower. The yield of the hydrazone is about 67% if the recovered imine is taken into account. 

Hexafluoroacetone imine has been prepared by the reaction of hexafluoroacetone with triphenyl phosphine imine,2 by the pyrolysis of N-phenyl-2,2-diaminohexafluoropropane,23 by the reaction of hexafluorothioacetone with hydrazoic acid,4 and by the reaction of ammonia and phosphorus oxychloride with hexafluoroacetone.4,5 The latter method, which is described here, is the most convenient for it does not require preparation of several intermediates or use of pressure equipment. This method has also been used to prepare the imines of other Huoroketones, including the imines of chloropentafluoroacetone, dichlorotetrafluoroacetone, and perfluorodiethyl ketone.5 Substitution of methylamine for ammonia in this procedure gives the N-methyl imine.5... 

Trifluoromethyl-l,2,4-triazoles 24 were obtained in good yields by the interaction of hexafluoroacetone imines 25 with HN3 (Scheme 24). 

An interesting concept for the preparation of seven-membered heterocycles with several heteroatoms was reported in 1988 by Burger and coworkers. Base-catalyzed reaction of hexafluoroacetone imine derivatives 53 with epichlorohydrine resulted in the formation of l,5-dioxa-3-azepines 54 and l-oxa-3,5-diazepines 55 (Fig. 10.24). ... 

FIGURE 10.35 Hexafluoroacetone imine-based synthesis of 1,3,-triazepines. 

Hexafluoroacetone imine also reacts with substitution of the imine hydrogen atom (eq 6). ... 

Fluoro-2-perfluoroalkyl-4-(trifluoromethyl)oxazoles were formed by reduction of perfluoroacyUmines with some metals. The reaction is promoted by catalytic amounts of Cul salts and crown ethers. Among the metals (magnesium, tin, aluminum, and zinc) only zinc and tin exerted as a defluorinating effect. The best yields of oxazoles were attained in the presence of zinc [22, 23]. A similar single electron transfer mechanism was described for cyclization of other hexafluoroacetone imines with metals. The role of crown ether is apparently reduced to the assistance in the elimination of ZnF with formation of 0-anion, which results in the intramolecular cyclization to oxazoles. 

Hexafluoroacetone imine distilled slowly during ca. 1 hr. into stirred anhydrous hydrazine cooled below 10°, allowed to warm to room temp., poured rapidly on P2O5, mixed and distilled -> hexafluoroacetone hydrazone (Conversion 53-59%) dissolved in benzonitrile, added dropwise with stirring during 1 hr. under Ng to ice-cooled Pb-tetraacetate and benzonitrile, then stirred 1 hr. at room temp. bis(trifluoromethyl)diazomethane (Y 76-79%). F. e. s. W. J. Middleton and D. M. Gale, Org. Synth. 50, 6 (1970). 

Perfluoroisopropylatnine, which was earlier reported to be formed when hexafluoroacetone imine is treated with hydrogen fluoride but could not be isolated, has been obtained as a liquid, stable in clean glassware at room temperature, by storage of the iminosulphur difluoride (21) over caesium fluoride at 20 "C ... 

Treatment of perfluoroisopropylamine with sulphur tetrafluoride in the presence of caesium fluoride at 90 °C yields the iminosulphur difluoride (CFslaCF-NiSFa, which can also be prepared from hexafluoroacetone imine and sulphur tetrafluoride. Treatment of (21) with sulphur tetrafluoride in the presence of caesium fluoride at 70 °C yields the iminosulphur difluorides (CFa)aCF-N SFa, (CFa)aaN SFa)a, and (CFa)2(FaS N)C-N S N-C(N SF,)-(CFala, while with phosphorus pentachloride at 0 C it yields the iminosulphur dichloride (CFa)aCCl-N SCla. Similarly, treatment of the trifluoroacetyl compound CFa-CO-N iSFa (formed, together with CaFj-N SFa and CFg-COF by reaction of trifluoroacetamide with sulphur tetrafluoride in the presence of sodium fluoride at 90 °C) with phosphorus pentachloride gives CFa CO N SClj. Treatment of hexafluoroacetone hydrazone with sulphur tetrafluoride in the presence of caesium fluoride at 0— 20 C yields... 

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