Fluorinated acetophenones

NMR spectra of dioxiranes derived from fluorinated acetophenones 29-36 using Oxone have also been reported <20030L2853>. The fluorine nuclei of CF3 group bonded to dioxirane ring typically resonates at —85 0.5 ppm. 

As a part of recent investigations in the chemistry of arylisoxazoles and arylpyrazoles, respectively used as herbicides (ref. 20) and fungicides (ref. 21), fluorinated acetophenones were prepared (ref. 22) following a similar methodology (Scheme 8) ... 

Ring-Substituted Acetophenones. Kirk and coworkers have shown the importance of fluorine substitution in the aromatic ting of several ring-fluorinated neutoactive amines (31). Due to their apparent importance, we undertook the asymmetric reduction of ring-fluorinated acetophenones with 1. The reduction of 2, 3, 4, 5, 6 -pentafluoroacetophenone with 1 provided the corresponding alcohol in... 

We were interested in flying DlP-Chloride for the enolboration-aldolization of ring-fluorinated acetophenones and benzaldehydes. During this research, we encountered a very interesting phenomenon. When we carried out the aldolization of diisopinocampheylboron enolate from 2 ,3, 4 ,S ,6 -pentafluoroacetophenone with pent uorobenzrddehyde at -78 °C, we obtained the product aldol, within 5 d, in 79%... 

The use of organic-solvent-free systems can be applied to the cyanohydrin synthesis of a wide range of acetophenone derivatives (Table 8.2) electronegative substituents (e.g. fluorine) facilitate high conversions and enantiomeric excess of the product, whereas electropositive substituents (e.g. methoxy-) result in low to no conversion into the corresponding cyanohydrins. 

The electrofluorination of acetophenone and benzophenone takes place in anhydrous HF and in the presence of solvents such as chloroform and acetonitrile [38]. The fluorination of the aromatic rings occurred to various extent. Further uses of anhydrous hydrogen fluoride as a liquid environment for electrofluorination processes have been reported, for example, by Matalin etal. [39]. In particular, systems with low conductivity in liquid hydrogen fluoride and nonselective processes have been studied and optimized. The fluorination of benzene and halobenzenes in the presence of Et4NF—(HF) in an undivided cell has been studied by Horio et al. [40] Cathodic dehalogenation is observed to accompany the anodic fluorination process. 

There are no reports of fluorination of acetophenone, but 2,2,2-trifluoro-t-phenylethanone and its homologs react with sulfur tetrafluoride at 100 150°C, even without addition of hydrogen fluoride, to give reasonable to good yields of fluoroalkylbenzcncs l.51... 

Selective polarographic reduction of a-C-F bonds in 2,2,2-trifluoro-l-phenylethanone is performed under high pH, while in acidic media the compound is reduced without loss of fluorine to the alcohol and the corresponding pinacol.98 l,2-Dimethyl-2-phenylbenzimidazole, which is a novel and efficient reducing agent, transforms 2,2,2-trifluoro-l-phenylethanone(8) effectively into acetophenone with high yield.99... 

Hydrogenation of 2,2,2-trifluoroacetophenone and its derivatives with a mixture of trans-RuCl2[(S)-xylbinap][(S)-daipen] and (CH3)3COK in 2-propanol gives the S alcohols quantitatively with a high optical purity (Scheme 1,64) [258]. Unlike with many chiral borane reagents [264], the sense of enantioface discrimination is the same as in hydrogenation of acetophenone. The electronic effects of 4 -substituents on the enantioselectivity are small. These chiral fluorinated alcohols are useful as components of new functionalized materials [265]. 

The rates at which several substituted benzenes quench triplet benzophenone have been measured 17 8). No single linear free energy relationship can be derived. For alkoxybenzenes, alkylbenzenes, benzene itself, and benzotrifluoride as quenchers, one finds a linear plot of log vs. IP with a slope similar to that found for the plot of all substituted benzenes and triplet a-trifluoroacetophenone. A given aromatic such as benzene quenches the fluorinated ketone triplet, which has an E - -E(A /A) value of only 16 kcal, some 50 times faster than it quenches triplet acetophenone or benzophenone 132>. This rate difference reflects only 20% of the full 12 kcal difference in thermodynamic redox potentials. However, the halobenzenes and benzonitrile quench triplet benzophenone faster than does benzene 178>. It seems likely that with these electron poor benzene derivatives, some alternate chemical reaction becomes dominant. Although a reverse CT process has been suggested, with the triplet ketone as donor, it is perhaps more likely that some sort of radical addition occurs with conjugating substituents on... 

Acetophenone, A/-methyloxazolidine derivative, lithiation, 56, 261 Acetyl hypofluorite fluorination of uracil by, 59, 3 fluorination using, 60, 7 reaction with pyridines, 58, 280, 289 Acetylacetone, hexafluoro-, reaction with ethylenediamine, 56, 3 Acetylene cyclic dimer, trimer. tetramer, dissociation energies, 56, 343 Acetylenes, activated reactions with 3-diazo-azoles, 59, 70... 

Phenol trimethylsilyl ether, fluorination of 647 Phenol-water complexes 145-169 Ph0H(H20)i 149-156 Ph0H(H20)2 149, 150, 152-155 Ph0H(H20)3 156-160 Ph0H(H20)4 160-169 Phenones—see Acenaphthoquinones, Acetophenones, Acrylophenones,... 

It can be seen that for 4 -trifluoromethyl acetophenone (entry 4), the initial rate is higher than for the other compounds. It seems that there is an activation of the ketone group by the three fluorine atoms through the aromatic ring. At the other end, no conversion was observed for isopropyl-formiate-benzoyle (entry 3) This can be attribute to the low activity of the a-keto-ester-group or because of the insolubility of the molecule in the polymer. 

The 13C NMR study clearly reveals that acetophenone largely shifts to the downfield when in association with BF3, while no shift is observed in trifluoroacetophenone under the same conditions. This fact suggests that no association of the markedly weak Lewis basic carbonyl group of 27 with Lewis acid is observed under the NMR analysis conditions. The nonfluorinated carbonyl group associates strongly with Lewis acid to enhance the electrophilic reactivity, while the corresponding fluorinated one does not (Scheme 1.19) [ 8]. 

Introduction of at least one fluorine atom to the methyl group of acetophenone leads to a dramatic change in configurational preference of the corresponding N-( l-phenethyl)imines (16, 17, and 18) from syn to anti, where the syn configuration of the methyl group to the N-phenethyl group is preferred in the parent nonfluorinated imine 15 (Scheme 1.79) [15]. The stereochemistry was confirmed by NOE analysis in H NMR for 16 and 17, and... 

Since the first asymmetric reduction of ketones with chiral borohydrides by Itsuno et al. [ 1 ], a number of studies on the asymmetric reduction of ketones with chiral borane reagents have been demonstrated [2]. Corey s oxazaborolidines are some of the most successful reagents [3 ]. The effect of fluorine substituents was examined in the asymmetric reduction of acetophenone with LiBH4 by the use of chiral boronates (73) obtained from substituted phenyl boronic acid and tartaric acid [4]. Likewise, 3-nitro, fluorine, and trifluoromethyl groups on the 3- or 4-position provided enhanced stereoselection (Scheme 5.20). 

Figure 15-28. Effect of introducing a fluorine atom or atoms at the a-position of acetophenone on the stereoselectivity in the reduction by G. candidum acetone powder11741.

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