Fluorinated alcohols, catalysis

Neumann R, Shaik S, de Visser SP, Kaneti J (2003) Fluorinated alcohols enable olefin epoxidationby H2O2 template catalysis. J Org Chem 68 2903-2912... 

A review has illustrated the importance of atomic-level DFT studies in elucidation of the function of hydrogen bonds in organocatalytic reactions through influence on the mechanism of substrate activation and orientation, and the stabilization of transition states and intermediates. Examples discussed include stereoselective catalysis by bifunctional thioureas, solvent catalysis by fluorinated alcohols in epoxidation by hydrogen peroxide, and intra-molecular cooperative hydrogen bonding in trans-a,a -(dimethyl-l,3-dioxolane-4,5-diyl)bis(diphenyl methanol) (TADDOL) (7)-type catalysts. ... 

As a consequence of the above summarized properties of fluorinated alcohols, they are ideal solvents for the generation of cationic or radical-cationic species or reaction intermediates. This eflect has been exploited numerous times, for example, in the investigation of organic radical cations [11]. At the same time, it lies at the heart of the catalysis of alkene epoxidation with hydrogen peroxide and of Baeyer-Villiger-type oxidations of carbonyl compounds. The mechanisms of the latter two reaction types are discussed in more detail in Sections 4.3.1.1 (epoxidation) and Section 4.5.1 (Baeyer-VUliger). 

Baeyer-Villiger Oxidation of Ketones in Fluorinated Alcohol Solvents - Catalysis by Arsonic and Seleninic Adds... 

It should be noted that the related imine-oxaziridine couple E-F finds application in asymmetric sulfoxidation, which is discussed in Section 10.3. Similarly, chiral oxoammonium ions G enable catalytic stereoselective oxidation of alcohols and thus, e.g., kinetic resolution of racemates. Processes of this type are discussed in Section 10.4. Whereas perhydrates, e.g. of fluorinated ketones, have several applications in oxidation catalysis [5], e.g. for the preparation of epoxides from olefins, it seems that no application of chiral perhydrates in asymmetric synthesis has yet been found. Metal-free oxidation catalysis - achiral or chiral - has, nevertheless, become a very potent method in organic synthesis, and the field is developing rapidly [6]. 

In the first step the alcohol moiety of 32 is protected as tert-butyldi-methylsilyl ether (TBS). The TBSOTf / 2,6-lutidine system is one of the most powerful methods for the formation of TBS ethers. This silyl protecting group is quite stable to a variety of organic reaction conditions and is cleaved under strong acidic or strong basic conditions, under Lewis acid catalysis and in the presence of a fluorine source (e.g. TBAF). In the second step the methyl ester is hydrolyzed using standard saponification conditions to give 33. 

Likewise, the competitive reaction of aldehydes 23 and 24 with allyltributylstannane gives homoallylic alcohol (25) exclusively (Scheme 1.18). In contrast, nonfluorinated cycloadduct is produced mainly under the catalysis of BF3 etherate in methylene chloride. These results clearly demonstrate that fluorinated carbonyl compounds are more reactive however, there is a turnabout in the reactivity under the Lewis acid catalytic conditions because of the lower basicity of the carbonyl group than that of the nonfluorinated one. 

Petrov, V.A. Reactions of 2,2-bis(trifluoromethyl)oxirane with alcohols under phase transfer catalysis. J. Fluorine Chem. 2004, 125, 531. 

Other experimental 157-nm resists can be considered to be derived from 193-nm CA resists. The homopolymer poly(HFIPA-norbomene) has an optical density of 1.8/)nm (130). First used in 193-nm resist polymers (131), HFIPA-norbomene monomer can be incorporated into cyclic olefin polymers prepared via organometalUc catalysis, and can be copolsrmerized with vinyl monomers such as acrylates or fluorinated acrylates using standard free-radical polymerization to give products with optical densities of less than 3/)um (Fig. 18, lower structure) (132,133). Still other fluorinated monomers can be employed in 157-nm resists, and resist systems based on polymers of fluorinated olefins and vinyl alcohols have been described (134,135). In general, it appears that incorporation of fluorine compromises the etch resistance of resists when compared with their hydrocarbon analogues (136). 

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