Ketones difluoro

Tedder and Walton [286] reviewed the kinetics of the reactions of halogenomethyl radicals in 1967. As regards mono- and difluoromethyl radicals, most of the data given in Table 24 have been obtained since that time. The commercial availability of the corresponding ketones, difluoro-... 

Perilla ketone — see Ketone, 3-furyl isopentyl Perillene synthesis, 4, 668 Perinones, 1, 327, 337 Periodinane, bromo-synthesis, 1, 571 Periodinane, difluoro-reactions, 1, 571 Periodinanes cyclic... 

The recent discovery of a convenient synthesis of sulfur tetrafluoride from sulfur dichloride and sodium fluoride in acetonitrile invited the application of this reagent in fluorination reactions. Hasek, Smith and Engelhardt showed that carboxylic acids and their derivatives can be converted into trifluoromethyl derivatives and that aldehydes and ketones are converted into 5 em-difluoro compounds. They also observed that the reaction was acid... 

Boswell,making use of the methodology elaborated by Martin and Kagan, prepared a series of 6,6-difluoro-A -3-ketones closely related to the steroid hormones, exemplified by the conversion of 3)5,17a-dihydroxypregn-5-en-20-one diacetate (7) to 6,6-difluoro-17a-acetoxyprogesterone (12). Reaction of (7) with nitrosyl fluoride at 0° affords the nitrimine (8), which is... 

In contrast to the above behaviour, the corresponding A -pyrrolidyl enamines (9) react with perchloryl fluoride in ether to furnish the 4,4-difluoro-A -3-ketones (10) contaminated with some of the 4-fluoro-A -3-ketones (11). Similar results are obtained with the corresponding 19-norsteroids... 

The reactions discussed above also lend themselves to efficient syntheses of 16-mono- and 16,16-difluoro-l7-ketones, l4-fluoro-A -20-ketones °... 

Diazoketones react with trifluoromcthyl hypofluorite to give a mixture of a,a-difluoro ketones and o-fluoro-a-trifluoromethoxy ketones [70, 71] With elemental fluorine, two fluorine atoms replace the nitrogen in both diazoketones and unactivated diazo eompounds [70, 72, 73] (equation 9)... 

Aryl ketone hydra ones are oxidized and fluonnated by fluorine to give a mixture of mono and difluoro hydrocarbons [74] (equation 10)... 

Most aliphatic [95, 184, 185, 186, 187], aromatic [95 186,188], md heterocyclic [189,190] ketones react with DAST in the usual way to give geminal difluoro derivatives Fluonnation of cycloaliphatic ketones, in particular, is often accompanied by a spontaneous dehydrofluorination to form considerable amounts of... 

The preparation of e/n-difluoro compounds by the oxidative fluorodesul-furization ot 1,3-dithiolanes readily proceeds by treatment with a pyridinium polyhydrogen fluoride-Af-halo compound reagent the latter serves as a bromonium ion source [2], l,3-Dibromo-5,5-dimethylhydantoin is the most effective of several At-halo oxidants. It is believed that /V-halo compounds combine with hydrogen fluoride to generate in situ halogen fluorides, the oxidants. Formation of gem-difluorides from dithiolanes derived from ketones is efficient and rapid, even at -78 °C, whereas the reaction of dithiolanes derived from aldehydes requires higher temperature (0 °C) (equation 4). 

The milder metal hydnde reagents are also used in stereoselective reductions Inclusion complexes of amine-borane reagent with cyclodexnins reduce ketones to opucally active alcohols, sometimes in modest enantiomeric excess [59] (equation 48). Diisobutylaluminum hydride modified by zmc bromide-MMA. A -tetra-methylethylenediamme (TMEDA) reduces a,a-difluoro-[i-hydroxy ketones to give predominantly erythro-2,2-difluoro-l,3-diols [60] (equation 49). The three isomers are formed on reduction with aluminum isopropoxide... 

The pyrrolidine enamines of /l -3.]cetosteroids (111), on alkylation with methyl iodide, gave mainly the N-alkylated product (5,55) in nonpolar solvents such as benzene. The reaction in more polar solvents gave the 4-methylated product (5.S). The reaction of (111) with perchloryl fluoride involves attack at the C-4 atom to give, after acid hydrolysis, either 4-fluoro-zJ -3-ketone (119) or 4,4-difluoro-zJ -3-ketone 120), depending on the reaction conditions (59). 

Kricheldorf et al. used trimethylsilylated phenols to react with activated difluoro monomers, such as DFBP, in the presence of catalytical amounts of CsF to prepare polyfether ketone)s.80,81 The polymers were prepared in the melt without solvent and can be directly processed. 

Many aldehydes and ketones have been converted to g m-difluoro compounds with sulfur tetrafluoride (SF4), " including quinones, which give 1,1,4,4-tetra-fluorocyclohexadiene derivatives. With ketones, yields can be raised and the reaction temperature lowered, by the addition of anhydrous HF. Carboxylic acids, acyl chlorides, and amides react with SF4 to give 1,1,1-trifluorides. In these cases the first product is the acyl fluoride, which then undergoes the ge i-difluorination reaction ... 

The indium-mediated aqueous Reformatsky reaction was used in the synthesis of a,a-difluoro- 3-hydroxy ketones (Eq. 8.93).236... 

In this reaction, the CH2C12/DMF solvent (9 1) suppresses the undesirable Claisen condensation and increases the yield of 2,2-difluoro-3-hydroxyesters. It is notable that high yields are obtained even with ketones and enolizable aldehydes, which do not undergo the Reformatsky reaction. 

A trifluoromethyl anion is also difficult to generate because it easily lose a fluoride ion to form difluoro carbene. Shono and Kashimura et al have similarly achieved the generation of such a species from trifiuoromethane using the electrogenerated a-pyrrolidone anion. The efficient trifluoromethylation of aldehydes and ketones in the presence of hexamethyldisilazane (HMDS) can thus be obtained (Scheme 4.3) [32]. 

Reaction of 1 with 4-fluorobenzoyl chloride yielded the difluoro-containing monomer 2, which is readily polymerized with a bisphenol using potassium carbonate in /V, /V-dimethy 1 acetamide to yield poly(ether ketone)s. The five poly-(ether ketone)s prepared were soluble in polar aprotic solvents and were cast into flexible, creasable films showing good thermal stability. We have demonstrated that 1 -phenoxy-substituted naphthalene moieties undergo a Friedel-Crafts acyla-... 

Hexafluoroisopropylidene-unit-containing aromatic poly(ether ketone)s were first synthesized from an alkaline metal salt of Bisphenol AF (1) and 4,4 -difluoro-benzophenone.14 Cassidy and co-workers prepared hexafluoroisopropylidene-unit-containing poly(ether ketone)s by condensing 2,2-bis[4-(4-fluorobenzoyl)-phenyl]-l,l,l,3,3,3-hexafluoropropane (9) and 2,2-bis[4-(4-fluorobenzoyl)-phenyljpropane (10) with Bisphenol AF (1) or Bisphenol A (4) (Scheme 7).15 The reactions are nucleophilic aromatic displacements and were conducted in DMAc at 155- 160°C with an excess of anhydrous potassium carbonate. After 3 to 6 h of reaction, high-molecular-weight poly(ketone)s are obtained in high yields. 

Bisphenol 4,4 -Difluoro- Poly(arylene benzo- ether ketone)... 

The carbonyl of aldehydes and ketones can be transformed into a gem-difluoro group. This transformation can be performed either directly with DAST or in an indirect manner by treating the corresponding thioacetal or hydrazone with an oxidant (NBS, dibromohydantoin, etc.) in the presence of a source of fluoride ions (e.g., HF-pyridin complex or TBABF prepared from TBAF and KHF2). ... 

Acylation of 179 with 2,2-difluoro-3-methyl-4-pentenoic acid anhydride yields ot-amino ketones 180 that can serve as intermediates to prepare pseudopeptides such as peptidyl ot,ot-difluoroalkylketones 181 (Scheme 7.54) or ketomethylene pseudo-peptides. ... 

In some cases, the product depends on the nature of the acylating agent. Acylation of 182 with 2,2-difluoro-4-pentenoic acid anhydride leads to acylation at C, whereas acylation with 2,2-difluoro-4-pentenoic acid choride yields the 5-acyloxyoxazole 185 as the major compound. The 5-acyloxyoxazole can be rearranged to the 5(47/)-oxazolone 183 upon treatment with 4-(dimethylamino)pyridme. Treatement of 183 with anhydrous oxalic acid promotes decarbonylation to give fluorinated a-amino ketones 184 (Scheme 7.55). Selected examples of 4-acyl-5(4//)-oxazolones are shown in Table 7.20 (Fig. 7.22). 

From the study of a microbially mediated oxidation of arteether 28b, sufficient quantities of 7a-hydroxy 180 and 15-hydroxy derivatives 182 were obtained to employ them as intermediates for the preparation of fluorinated compounds. The hydroxyl groups were oxidized to the corresponding aldehyde 187, or ketone 188, with catalytic quantities of tetra- -propylammonium perruthenate (TPAP) in the presence of excess iV-methylmorpholine A -oxide. On reaction with DAST, 187 and 188 were converted into the corresponding geminal difluoro derivatives, 189 (63%) and 190 (42%). In addition to 190, a monofluoro olefin 191 was obtained in 25% yield from 188 on reaction with DAST <1995JME4120>. 

Chlorodifluoromethylketones underwent aldol reactions (Eq. 124) via zinc enolates, to afford good yields of a,a-difluoro-/ -hydroxy ketones, in a study by the Kyoto group [327]. Copper(I) or silver salt catalysis was essential and boron-trifluoride additive appeared to exert a key role in the conversion to the enolate. Earlier [328], chlorodifluoromethyl ketones had been converted to the di-fluoroenoxy silanes by the action of zinc in the presence of chlorotrimethyl silane. A difluoroenoxy silane was used by McCarthy and co-workers [329] to synthesise a kynureninase inhibitor (Eq. 125) Lewis acid-mediated reaction with a chloroglycinate installed the key carbon-carbon bond. 

Further, by using Et3N.3HF in acetonitrile as solvent, they have demonstrated that electrolysis of benzyl nitriles, carboxylic acid esters, sulphonic acid esters and ketones give the corresponding monofluoro- or difluoro-compounds, depending on anode potential in yields of 30 - 70 %. 

Yoshigama and Fuchigami have also reported that several dithioacetals of aliphatic and alicyclic ketones can be converted to their gem difluoro-derivatives in a similar manner. However, they found that with diphenyl dithioacetals only one C - S bond is cleaved to give the monofluoro- compound... 

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