Alcohols, reaction with hexafluoroacetone

Rearrangements arc common in reactions of sulfur tetrafluoride with acetylenic and allylic alcohols. Highly acidic acetylenic alcohols derived from hexafluoroacetone and other haloacetones react readily at ambient temperature to give fluorinated allenes 10 as the sole... 

Reactions with fluoride ion With the exception of CF3OH (see the next section), fluorinated alcohols of the type RpCF20H are not known [124] but complexes of K, Rb, Cs, Ag or (C2H5)4N+ fluorides with hexafluoroacetone have been isolated [125, 126], following from the earlier isolation of some similar complexes with carbonyl fluoride [127]. These complexes have been reasonably formulated as fluorinated alkox-ides (Figure 8.27), but the use of these salts in synthesis is often difficult because the complexes may also act as fluoride-ion donors [128]. 

Other methods that have been less regularly used are the dehydration of alcohols with dimethyl sulfoxide to form symmetrical ethers,62 the photochemical transformation of benzylic chlorides with tert-butyl alcohol,63 or radical reactions of hexafluoroacetone with alkanes.64 Mercury acetate promoted couplings of alcohols with vinyl acetate or vinyl ethyl ether to form vinyl... 

More is known of the chemistry of perfluoropinacol (H2PFP), first prepared in the reaction between hexafluoroacetone and isopropyl alcohol. An alternative and sometimes synthetically more useful procedure involves the reductive coupling of hexafluoroacetone with an alkali metal in a non-aqueous solvent such as THF (equation 42). By metathetic reactions involving Na PFP, a variety of perfluoropinacolate derivatives of the main group elements (B, Si, Ge, Sn and S) were prepared. Since perfluoropinacol is acidic (pA, = 5.95) and the anion quite stable to water, a variety of salts were prepar according to equation (43). ... 

Some reduction to the secondary alcohol, (CF3)2CHOH, also occurs as a side reaction. The reaction of hexafluoroacetone with methylarsine is more complex. It might be expected that tetramethyldiarsine and hexafluoroacetone would yield compound (III), however, this is not so... 

The 10-57-5-hydridosiliconate ion 62 is known in association with lithium,323 tetrabutylammonium,101 and bis(phosphoranyl)iminium93 cations. It is synthesized by hydride addition to the 8-.S7-4-silane 63, which is derived from hexafluoroacetone.101 Benzaldehyde and related aryl aldehydes are reduced by solutions of 62 in dichloromethane at room temperature101 or in tetrahydrofuran at 0°96 within two hours. The alkyl aldehyde, 1-nonanal, is also reduced by 62 in tetrahydrofuran at O0.96 Good to excellent yields of the respective alcohols are obtained following hydrolytic workup. The reactions are not accelerated by addition of excess lithium chloride,96 but neutral 63 catalyzes the reaction, apparently through complexation of its silicon center with the carbonyl oxygen prior to delivery of hydride from 62.101... 

Although intermolecular ene reactions of electron deficient ketones such as hexafluoroacetone, methyl pyruvate and diethyl oxomalonate are well-known, h2i ene reactions of simple ketones are virtually unknown. Ketones are less electrophilic than aldehydes and the ene adducts are tertiary alcohols which are much less stable than the secondary alcohols produced from aldehydes. We have found that ene adducts can be isolated from the EtAlQ2 catalyzed reactions of cycloalkanones and reactive ene components— 1,1-disubstituted alkenes with one end of the double bond sterically accessible and the other end capable of stabilizing a positive charge in an intermediate. 22 The yields are moderate at best (6-55%), but the reaction does provide an extremely simple route to homoallylic tertiary alcohols. 

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