Fluorous catalytic acetalization reaction

Using a fluorous palladacycle catalyst 10 originating from the corresponding fluorous Schiff base and palladium acetate, a fluorous Mizoroki-Heck reaction was achieved with an excellent turnover number (Scheme 12). A homogeneous catalytic reaction system was obtained when DMF was used as the solvent. After the reaction, perfluorooctyl bromide was added to facilitate the separation of DMF (containing the products and amine salts) from the catalyst phase. The resulting lower fluorous layer was condensed under vacuum and the catalyst residue was used in a second run. In this reaction, the palladacycle catalyst appears to act as a source of palladium nanoparticles, which are thought to be the dominant active catalyst. 

Bayardon and Sinou have reported the synthesis of chiral bisoxazolines, which also proved to be active ligands in the asymmetric allylic alkylation of l,3-diphenylprop-2-enyl acetate, as well as cyclopropanation, allylic oxidations and Diels-Alder reactions. [62] The ligands do not have a fluorine content greater than 60 wt% and so are not entirely preferentially soluble in fluorous solvents, which may lead to a significant ligand loss in the reaction system and in fact, all recycling attempts were unsuccessful. However, the catalytic results achieved were comparable with those obtained with their non-fluorous analogues. 

A copper catalysed click (azide-alkyne cycloaddition) reaction has been used to prepare a fluorous-tagged TEMPO catalyst (Figure 7.20). TEMPO is a stable organic free radical that can be used in a range of processes. In this case, its use in metal-free catalytic oxidation of primary alcohols to aldehydes using bleach as the terminal oxidant was demonstrated. The modified TEMPO can be sequestered at the end of the reaction on silica gel 60 and then released using ethyl acetate for reuse in further reactions in this way the TEMPO was used four times with no loss in activity. 

Recently, the present authors have achieved a facile recycling method for both catalyst and reachon medium using F-626 in a Mizoroki-Heck arylation reaction of acrylic acids [11]. The procedure employed a fluorous carbene complex, prepared in situ from a fluorous imidazolium salt, palladium acetate as the catalyst and F-626 as a single reaction medium. When acrylic acid was used as a substrate, separation of the product from the reaction mixture was performed simply by filtration with a small amount of FC-72. The FC-72 solution containing the fluorous Pd-catalyst and F-626 was evaporated and the residue containing the catalyst and F-626 (96% recovery) can be recycled for the next run (Scheme 3.5-6). They tried to reuse the catalyst, and observed no loss of catalytic activity in five re-use cycles. 

Pozzi, Sinou, and co-workers prepared a fluorous chiral phosphine, (R)-2- bis[4-(1 H,1 H-perfluorooctyloxy)phenyl]phosphino -2 -(l H,1 H-perfluorooctyloxy)-l, 1 -binaphthyl (F content = 52%, partition coefficient n-perfluorooctane/toluene = 0.23, n-perfluorooctane/CHjOH = 7.42) and used for a chiral ligand of palladium complex in an asymmetric aUyHc alkylation of 1,3-diphenylprop-2-enyl acetate [8]. The reaction was carried out at room temperature in BTF or toluene and gave the corresponding product in 99% and 88% chemical yields and 81% ee and 87% ee, respectively after the nonfluorous MOP complex gave the product in 95% yield and 99% ee in toluene at 0 °C [9]) [Eq. (1)]. When toluene was used as a solvent, the simple extraction of the reaction mixture with n-perfluorooctane (twice) allowed the complete removal of the ligand and of the palladium complex. However, the recovered palladium complex did not have catalytic activity for the reachon. 

The reactions in water can be facilitated with an amphiphilic surfactant. Inamoto eial. [105] used these conditions in a catalytic Chan-Lam-Evans arylation of imidazoles with copper(II) acetate and 10 mol% of l,l -dimethyl-2,2 -dipyridyl or its fluorous derivative as ligands at room temperature under air. The best surfactants were BrijSO, Triton-X-100, and the fluorous-type surfactant F-PEG. 

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