Perfluoroalkyl alkyl ketones

Silyl enol ethers have also been used as a trap for electrophilic radicals derived from a-haloesters [36] or perfluoroalkyl iodides [32]. They afford the a-alkylated ketones after acidic treatment of the intermediate silyl enol ethers (Scheme 19, Eq. 19a). Similarly, silyl ketene acetals are converted into o -pcriluoroalkyl esters upon treatment with per fluoro alkyl iodides [32, 47]. The Et3B/02-mediated diastereoselective trifluoromethylation [48,49] (Eq. 19b) and (ethoxycarbonyl)difluoromethylation [50,51] of lithium eno-lates derived from N-acyloxazolidinones have also been achieved. More recently, Mikami [52] succeeded in the trifluoromethylation of ketone enolates... 

A one-pot synthesis of alkyl perfluoroalkyl ketones has been developed. Phosphoranes, generated in situ, are acylated with a perfluoroacyl anhydnde, and the resultmg phosphonium salts are hydrolyzed with alkali [4S (equation 48) Hydrolysis of a carbon-sulfur bond in 2-chloro-2,4,4-trifluoro-1,3-dithietane-S-trioxide, which can be obtained from 2,2,4,4-tetrachloro-l,3-dithietane by fluor-mation with antimony trifluoride followed by selective oxidations, opens the nng to produce 2-chloro-1,1,2-trifluorodimethyl sulfone [49] (equation 49)... 

The haloform reaction of unsymmetrical perfluoroalkyl and co-hydroper-fluoroalkyl trifluororaethyl ketones gives the alkane corresponding to the longer alkyl chain [54] (equation 53) If the methyl group contains chlorine, the reaction can take different pathways, leading to loss of chlorine (equation 54), because of the variable stability of the chlorine-substituted methyl carbanions in alkali. 

Rate constants and Arrhenius parameters for the reaction of Et3Si radicals with various carbonyl compounds are available. Some data are collected in Table 5.2 [49]. The ease of addition of EtsSi radicals was found to decrease in the order 1,4-benzoquinone > cyclic diaryl ketones, benzaldehyde, benzil, perfluoro propionic anhydride > benzophenone alkyl aryl ketone, alkyl aldehyde > oxalate > benzoate, trifluoroacetate, anhydride > cyclic dialkyl ketone > acyclic dialkyl ketone > formate > acetate [49,50]. This order of reactivity was rationalized in terms of bond energy differences, stabilization of the radical formed, polar effects, and steric factors. Thus, a phenyl or acyl group adjacent to the carbonyl will stabilize the radical adduct whereas a perfluoroalkyl or acyloxy group next to the carbonyl moiety will enhance the contribution given by the canonical structure with a charge separation to the transition state (Equation 5.24). 

Perfluoroalkyl lithium reagents undergo reactions typical of their hydrocarbon analogs. For example, perfluoroalkyl lithium reagents generated in situ from perfluoroalkyl iodides and alkyl lithiums reacted readily with aldehydes and ketones to yield the corresponding secondary and tertiary carbinols, and with esters to give either ketones or tertiary carbinols [12]. No 1,4-addition product is observed when a,/ -unsaturated ketones and esters are employed. 

This assertion is borne out by the small deviations from fluid-isotropiclike values of the photoproduct ratios found in the Norrish II reactions of the two alkyl perfluoroalkyl ketones 76 (with m, n = 7,8 and 9,10) in the (macroscopically) highly ordered smectic phases of F10H10 [273,274]. As... 

Soloshonok and co-workers have developed a method for the synthesis of a-(perfluoro-alkyl)amines from perfluoroalkyl carbonyl compounds by a transamination involving an azomethine a/omethine (Schiffbase) isomerization. They call this method a biomimetic, base-catalyzed 1,3-proton shift reaction, and have applied it to perfluoroaldehydes,12-15 perfluoroalkyl ketones,12 18 / -(perfluoroalkyl)-/l-oxo esters,15 16 19 24 and - -( perfluoroalkyl)-a-oxo es-ters2 " -26 to synthesize the corresponding a-(perfluoroalkyl)amincs, / -(perfluoroalkyl )-/i-amino acids, and 3 -(perfluoroalkyl)- x-amino acids. 

The haloform reaction of unsymmctrical perfluoroalkyl and m-hydroperfluoroalkyl trifluoro-methyl ketones 6 gives the alkanes 7 corresponding to the longer alkyl chain.174... 

Alkylation. Zinc-mediated reaction of cinnamyl chloride with aldehydes and ketones in aqueous THE" and Barbier-type reactions involving perfluoroalkyl... 

Couplings. Partially fluorinated allyl ketones and 1 -alkenes are formed by the Stillc coupling of P-perfluoroalkyl-substitued alkyl iodides with organostannanes with or without the presence of CO, ... 

Kitazume and Ishikawa have published a number of communications on the regiospecific zinc mediated perfluoroalkylation of a variety of substrates [148-151]. A compilation of these results appeared in 1985 [152] (Scheme 71). Secondary alcohols are available in moderate yield by reaction of perfluoro-alkyl halides (RpX) with aldehydes as the result of a modified Barbier-type reaction [148-152]. However, reaction with ketones gave low yields of the expected tertiary alcohols, although the yields could be doubled by reaction in the presence of a bis[7i-cyclopentadienyl]titanium(II) catalyst, which was prepared in situ by reduction of the dichloride with zinc in the presence of ultrasound. 

Full details have been published of the use of chldrofluoromethylenetri-phenylphosphorane, generated in situ from sodium dichlorofluoroacetate and triphenylphosphine or from dichlorofluoromethane, potassium t-butoxide, and triphenylphosphine, in the synthesis of olefins of the type RfRC CFC1 (Rp = perfluoroalkyl or CFuCl R = alkyl, aryl, or aralkyl) from appropriate ketones. ... 

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