Perfluoroalkylation enantioselective

Addition of HSiMeCl2 to cyclopentadiene is catalyzed by (42) at room temperature at low catalyst loading (0.01 mol.%) to give the (S)-allylsilane in moderate ee.125 This enantioselectivity can be enhanced dramatically with incorporation of perfluoroalkyl groups into the amine functionality (Scheme 26).126... 

The C02-philic perfluoroalkyl-substituted (R,S)-3-H F -BINAPHOS ligand [34] was successfully applied to enantioselective hydrogenation in the inverted SCCO2/H2O system. The complex [Rh(cod)2]BARF was chosen as metal source and the active catalyst was formed in situ. Using the same procedure as above, similar activities and more than 98% ee were obtained consistently over five subsequent cycles in the hydrogenation of methyl 2-acetamido acrylate. The results demonstrate the potential of the inverted SCCO2/H2O system for asymmetric synthesis of chiral biologically active products. 

A diphenylprolinol derivative, having hydrophobic perfluoroalkyl phase tags, has been synthesized and used as a pre-catalyst to generate in situ a fluorous oxaz-aborolidine catalyst for the reduction of prochiral ketones with borohydride. The system afforded high enantioselectivities and the pre-catalyst is easily separated and recycled.272 Reduction of enantiopure A-p-toluenesulfinyl ketimines derived from 2-pyridyl ketones with sodium borohydride affords A-p-toluenesulfinylamines with good yields and diastereoselectivities.273... 

Francio G, Wittmann K, Leitner W (2001) Highly efficient enantioselective catalysis in supercritical carbon dioxide using the perfluoroalkyl-substituted ligand (R, S)-3-H2F6-BINAPHOS. J Organomet Chem 621(1-2) 130-142... 

To overcome a main problem eissociaied with homogeneous catalysis, i.e. the recovery of the catalyst, the latest development in this field comprises the functionalization of catalyst precursor 1—3 with perfluoroalkyl chains to enable catalysis to be carried out in an txganic/perfluorinated two-phase solvent system. It has been demonstrated that this approach allows reuse of the catalyst several times. Recently, an elegant synthetic route towards the enantioselective synthesis of chiral allylic alcohols in which... 

The chiral ferrocenylmonophosphine ligand 7c, which is analogous to PPFA 3a but contains a perfluoroalkyl group on the aminoethyl side chain, is more enantioselective than PPFA (Scheme 2-48) [67]. The enantioselectivity in the palladium-catalyzed hydrosilylation of cyclopentadiene and 1-vinylcyclohexene is increased to 60% ee and 43% ee, respectively. The polymer-supported PPFA 62 has been used for the hydrosilylation of styrene (15% ee) [68]. 

Neutral catalysts or catalyst precursors based on fluorinated ligand systems have been applied in compressed CO2 to a broad range of transformations such as Zn- and Cr-catalyzed copolymerization of epoxides and CO2 [53, 54], Mo-catalyzed olefin metathesis [9], Pd-catalyzed coupling reactions [43, 55, 56] and Pd-catalyzed hydrogen peroxide synthesis [57]. Rhodium complexes with perfluoroalkyl-substituted P ligands proved successful in hydroformylation of terminal alkenes [28, 42, 44, 58], enantioselective hydroformylation [18, 59, 60], hydrogenation [61], hydroboration [62], and polymerization of phenylacetylene... 

Scheme 2.105 Enantioselective perfluoroalkylation [30] using perfluoroalkyl halides with chiral auxiliary groups [31].

Arylzinc thiolate complex 20 containing perfluoroalkyl chains was prepared as a model catalyst precursor for the enantioselective zinc-mediated 1,2-addition of Et2Zn to benzaldehyde in fluorous biphasic systems. The addition reaction to benzaldehyde was first carried out in hexane to give 94% ee compared with 72% ee for the original non-fiuorous catalyst. When the reaction was carried out in an octane/perfluoromethylcyclohexane biphasic system, the catalyst immobilized in the fluorous phase could be used twice without loss of enantioselectivity, but the system was less efficient from the third run (Scheme 23). 

Cationic iridium(i) complexes with chiral phosphinodihydrooxazoles modified with perfluoroalkyl groups on the ligand and BARF counteranion catalyze the enantioselective hydrogenation of A-(l-phenylethylidene)aniline in SCCO2 (Scheme 9). (Tf)-A-phenyl-l-phenylethylamine 6 is formed quantitatively with up to 81% ee, and the rate in SCCO2 is much faster than that in CH2CI2. Furthermore, the extractive properties of SCCO2 enabled product separation and catalyst... 

The merging of photoredox catalysis with asymmetric organocatalysis was reported by MacMillan and Nicewicz in 2008 [104]. Initial studies in the MacMillan group were devoted to the imidazolidinone-catalyzed asymmetric a-functionaliza-tion of aldehydes with a-bromo ketones and esters [104a] and were subsequently expanded to enantioselective perfluoroalkylations [105] and benzylations [106]. The... 

One year later, an extension of organo-photoredox catalysis into enantioselective a-trifluoromethylation and a-perfluoroalkylation of aldehydes was reported by MacMillan and co-workers [150, 151] that was accomplished by using a readily available iridium photocatalyst [Ir(ppy)2(dtb-bpy)]" and a commercial imidazolidinone catalyst (Scheme 8.38). A broad range of perfluoroalkyl iodides and bromides as well as a variety of aldehydes bearing various functional or bulky groups afforded corresponding a-fluoroalkylated products in high yields with excellent diastereo-and enantioselectivity (up to 99% ee). 

Several experimental studies of the asymmetric Rh-catalysed cyclopropanation of alkenes with diazocompounds as rhodium carbenoid precursors have been reported. The perfluoroalkylated dirhodium complex (44) has proved efficient for catalysing the reaction between aryldiazocompounds and electron-rich styrenes on enol ethers with a good cw-diastereoselectivity but poor enantioselectivity. The dirhodium complexes (45) and (46), have both permitted the successful cyclopropanation of 0 -diazopropionates (47) and of diverse doubly stabilized diazocompounds (48). Both (45)/(47) and (46)/(48) combinations thus enabled formation of valuable cyclopropanes possessing at least one quaternary carbon in good yields and high diastereo- and enantio-selectivities. Noteworthy is that in the case of (48), the paramethoxyaryl-ketone moiety has been found to play a key role in the stereoinduction process. 

The application of fluorinated media seems to be a flourishing new area in homogeneous catalysis (103). However, until now enantioselective catalytic reactions in this alternative solvent are very rare. Chiral perfluoroalkylated SALEN-manganese complexes have been used for asymmetric epoxidation (104). 

Aminodiphosphane (P,N,P)-ligands form active catalysts with iridium(I) for transfer hydrogenation (249). A novel phosphino-dihydrooxazol, modified with perfluoroalkyl groups proved to be excellent ligand for enantioselective hydrogenation in supercritical carbon dioxide (250). 

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