Fluorous alcohol

Begue and coworkers recently achieved an improvement in this method by performing the epoxidation reaction in hexafluoro-2-propanol [120]. They found that the activity of hydrogen peroxide was significantly increased in this fluorous alcohol, in relation to trifluoroethanol, which allowed for the use of 30% aqueous H202. Interestingly, the nature of the substrate and the choice of additive turned out to have important consequences for the lifetime of the catalyst. Cyclic dis-ubstituted olefins were efficiently epoxidized with 0.1 mol% of MTO and 10 mol%... [Pg.217]

Fluoroalkyl Glycosides (RFn-(CH2)2-n-0-sugar) and Perfluor-oalkylidene Acetals Derived from Sugars The very low nucleophilicity of fluoroalcohols makes it difficult to substitute of a hydroxyl (anomeric or not). ° This is the reason why this type of ether is not very common. Such ethers have only been isolated in very small quantities in solvolysis reactions, or in carben insertions, performed in fluorous alcohols.Preparation of these ethers has been solved by means of the Mitsunobu reaction. This reaction is known to be dependent on the pA a of the acceptor of the glycosyl the acidity of fluorous alcohols allows a much easier deprotonation than with non fluorinated alcohols." ... [Pg.211]

The synthesis of proline-fused heterocyclic systems by 1,3-dipolar cycloaddition has been well-established in solution-phase synthesis (Scheme 14) [42]. It is usually performed as a one-pot, three-component reaction of a dipo-larophile with an in situ prepared azomethine ylide. Perfluoroalkanesulfonyl protected hydroxybenzaldehydes [43] or fluorous alcohol protected amino esters [44] have been developed as two different fluorous components for the synthesis of proline derivatives 11 and 12. [Pg.158]

An improvement employed the H202/MTO/fluorous alcohol system (described earlier) in a one-pot procedure for synthesis of mixed tetroxanes, which did not require isolation of the unstable and potentially explosive gem-dihydroperoxide intermediate 240. The more reactive carbonyl compound was first oxidized to the gi OT-dihydroper-oxide 240, followed by the addition of the less reactive carbonyl compound in the presence of 1 equiv of HBF4. This procedure afforded unsymmetrical tetroxanes 238 in good yields (method B, Scheme 45 Table 4) <2003TL6309>. [Pg.775]

Section IV of Table 3.6 lists several simple fluorous alcohols. The short-chain or Rf i/Rf2 alcohols in entries IV-2 and IV-3 show very poor fluorous phase affinities. As the perfluoroalkyl segment lengthens in the series Rf6(CH2)30H, Rfg(CH2)30H and Rfio(CH2)30H (entries IV-5, rV-7, IV-8), the fluorophilicities increase from 55.9 44.1 to 19.5 80.5. As expected, when a methylene group is removed from the first two compounds, the fluorophilicities also increase (47.4 52.6 and 26.5 73.5 entries IV-4, IV-6). Similar trends are found with all other functional groups in Table 3.6. [Pg.71]

Fluorous tertiary alcohols were prepared and applied as protecting groups of carboxylic acids. The fluorous alcohols were reacted with phenylacetic acid and... [Pg.102]

Huorous compounds are also potentially useful as additives to promote organic reactions in carbon dioxide. For example, a fluorous alcohol RfCH20H assists asymmetric hydrogenations with non-fluorous ruthenium BINAP catalysts, and a fluorous aryl alkyl ether (C8F17C6H4-P-OC12H25) does so in scandium-triflate-catalyzed aldol and Friedel-Crafts reactions. These additives are presumed to act as solubilizers or emulsifiers to promote contact among the various reaction components. Since they are fluorous, they can be readily recovered from the otherwise organic reaction mixtures for reuse. [Pg.112]

Abstract The quinoxaline (Qx) nucleus is present in various bioactive molecules. Thus, synthesis of Qxs continues to draw the attention of synthetic oiganic/medici-nal chemists. The contemporary interest in search for newer synthetic methods for this privileged class of compounds rcmains unabated and a vast number of publications continue to appear. The focus of this chapter is on the research woiks pubhshed in this area after the year 2000 with the inherent objective to attain sustainability towards the synthesis. The attention will be on the key sustainable approaches of pharmaceutical industries like the solvent-fiee reactions, use of alternate reaction media (e g., water, fluorous alcohols, polyethylene glycols, and ionic liquids), and alternate modes of synthesis such as microwave-assisted synthesis and flow reactions. [Pg.37]

Chebolu R, Kommi DN et al (2012) Hydrogen-bond driven electrophilic activation for selectivity control the scope and limitations of fluorous alcohol promoted selective formation of 1,2-disubstituted benzimidazoles and mechanistic insight for rational of selectivity. J Org Chem 77 10158-10167... [Pg.65]

Dinitrogen-fused heterocycles have been formed in high yield by thermal 3-1-2-cycloadditions of two types of azomethine imines with allenoates. Rhodium-catalysed formal 3 -l- 2-cycloadditions of racemic butadiene monoxide with imines in the presence of a chiral sulfur-alkene hybrid ligand have furnished spirooxindole oxazolidines and 1,3-oxazolidines stereoselectively. ° Formation of 1,2-disubstimted benzimidazoles on reaction of o-phenylenediamine with aldehydes is promoted by fluorous alcohols that enable initial bisimine formation through electrophilic activation of the aldehyde. [Pg.12]

Figure 6.27. Conjugate addition of benzyl alcohol to methyl propiolate catalysed by a fluorous phosphine...

The team of Crooks is involved in the synthesis and the use of dendrimers and, more particularly, poly(amidoamine) dendrimers (PAMAM), for the preparation of dendrimer-encapsulated mono- or bimetallic nanoparticles of various metals (Pt, Pd, Cu, Au, Ag, Ni, etc.) [55, 56]. The dendrimers were used as nanocatalysts for the hydrogenation of allyl alcohol and N-isopropylacrylamide or other alkenes under different reaction conditions (water, organic solvents, biphasic fluorous/or-ganic solvents or supercritical COz). The hydrogenation reaction rate is dependent on dendrimer generation, as higher-generation dendrimers are more sterically... [Pg.225]

The first demonstration of fluorous synthesis was in the preparation of small (8-12 members) isoxazo-line and isoxazole libraries by the three-step procedure outlined in Figure 8.1461 All reactions were purified by three-phase liquid-liquid extraction. The starting substrates were simple allylic alcohols which were tagged with the fluorous silyl halide 5 to make substrates 6 for an ensuing dipolar cycloaddition. This was conducted by the Mukaiyama method with a large excess of nitro compound and... [Pg.32]

D. P. Curran, Z. Luo, Rapid, Parallel Synthesis of Homo-allylic Alcohols by Lewis Acid Mediated Allylations of Aldehydes with New Fluorous Allyl Stannanes , Med Chem. Res. 1998, 8,261. [Pg.37]

A similar reaction has been conducted under fluorous biphasic conditions, using a perfluoroalkylated bipyridine as ligand to ensure that the copper species resides in the fluorous phase [22], The oxidation of a range of primary alcohols to the corresponding aldehydes was found to be possible, an example of which is shown in Scheme 9.11. The catalyst could be successfully recycled by phase separation, with analytically pure products being isolated even after... [Pg.188]

A fluorous analogue of DMSO has been used to perform Swern reactions [24], This widely used method of oxidizing an alcohol to an aldehyde falls down seriously from the environmental point of view due to its production of a stoichiometric amount of dimethyl sulfide. Here, a fluorous sulfoxide is prepared and used in the oxidation of several alcohols in dichloromethane, as shown in Scheme 9.12. After reaction, the sulfide is extracted into perfluorohexane and the system recycled. Unfortunately, extraction from dichloromethane was found to be difficult, but replacing the dichloromethane with toluene leads to a more efficient recovery. [Pg.189]

The effectiveness of 5a as a catalyst for the addition of alcohols 2 to propio-late 3 was first established under conventional fluorous Uquid/organic biphase conditions. This set the stage for the sequence in Fig. 3. Compounds 2a, 3, and 5a were combined in n-octane at room temperature in a 2.0 1.0 0.1 ratio (10 mol% 5a). As would be expected from Fig. 2, there was no visually... [Pg.72]

Neumann and Fish have studied the novel polyoxometalate salt 25, which features 12 fluorous ammonium cations [12]. This material was insoluble in EtOAc (and toluene) at room temperature, but dissolved at 80 °C to give an effective catalyst system for the oxidation of alkenes and alcohols by 30% aqueous H2O2. CooHng precipitated the catalyst, which was reused. Additional examples of thermomorphic fluorous catalysts have been briefly described in meeting abstracts [60,61] and will Hkely soon appear in the peer-reviewed literature. [Pg.86]

To date, reports have involved palladium catalysts for Suzuki and Sono-gashira coupling reactions [63-66], rhodium catalysts for silylations of alcohols by trialkylsilanes [67,68], and tin-, hafnium-, and scandium-based Lewis acid catalysts for Baeyer-Villiger and Diels-Alder reactions [69]. Regardless of exact mechanism, this recovery strategy represents an important direction for future research and applications development. Finally, a particularly elegant protocol where CO2 pressure is used instead of temperature to desorb a fluorous rhodium hydrogenation catalyst from fluorous silica gel deserves emphasis [28]. [Pg.86]

The catalyst remains in the fluorous phase, whilst the product is completely extracted, and secondary alcohol can be prepared by H2O2 oxidation. The catalyst solution can be recycled several time without loss of activity. [Pg.39]

A series of pseudo-C or pseudo-C2 symmetric complexes 168-171 (Fig. 27) exhibited isotactic predominance P = 0.50-0.75) however, the isotacticity is compromised in solvent-free bulk polymerization at 130 °C [129]. Fluorous tertiary alcohol ligands with electron-withdrawing CF3 group are weakly basic and thus expected to reduce the possibility of catalyst deactivation by bridged species formation. Al complexes 172 and 173 offered highly isotactic-enriched stereoblock PLA (Pm = 0.87) from ROP of rac-lactide [168]. [Pg.268]

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