Photocatalytic Palladium-Catalyzed Fluoroalkylation of Styrene Derivatives (original) (raw)
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The late-stage fluorination of common synthetic building blocks and drug leads is an appealing reaction for medicinal chemistry. In particular, fluorination of benzylic C-H bonds provides a means to attenuate drug metabolism at this metabolically labile position. Here we report two complimentary strategies for the direct fluorination of benzylic C-H bonds using N-fluorobenzenesulfonimide and either a decatungstate photocatalyst or AIBN-initiation.
Journal of the American Chemical Society, 2021
This Article describes the development of a decarbonylative Pd-catalyzed aryl-fluoroalkyl bondforming reaction that couples fluoroalkylcarboxylic acid-derived electrophiles [R F C(O)X] with aryl organometallics (Ar-M'). This reaction was optimized by interrogating the individual steps of the catalytic cycle (oxidative addition, carbonyl de-insertion, transmetalation, and reductive elimination) to identify a compatible pair of coupling partners and an appropriate Pd catalyst. These stoichiometric organometallic studies revealed several critical elements for reaction design. First, uncatalyzed background reactions between R F C(O)X and Ar-M' can be avoided by using M' = boronate ester. Second, carbonyl de-insertion and Ar-R F reductive elimination are the two slowest steps of the catalytic cycle when R F = CF 3. Both steps are dramatically accelerated upon changing to R F = CHF 2. Computational studies reveal that a favorable F 2 C-H-X interaction contributes to accelerating carbonyl de-insertion in this system. Finally, transmetalation is slow with X = difluoroacetate but fast with X = F. Ultimately, these studies enabled the development of an (SPhos)Pd-catalyzed decarbonylative difluoromethylation of aryl neopentylglycol boronate esters with difluoromethyl acetyl fluoride.
Photocatalytic fluoroalkylation reactions of organic compounds
Organic & Biomolecular Chemistry, 2015
Photocatalytic methods for fluoroalkyl-radical generation provide more convenient alternatives to the classical perfluoroalkyl-radical (Rf) production through chemical initiators, such as azo or peroxide compounds or the employment of transition metals through a thermal electron transfer (ET) initiation process.
Tetrahedron, 2015
An efficient protocol for Pd-catalyzed 2,2,2-trifluoroethoxylation of activated aryl bromides and bromochalcones has been developed. We unveil a fascinating insight into the Pd-catalyzed CeO cross-coupling reaction. Pd/tBuXPhos (L1) ligand system facilitates the CeO cross-coupling reaction between 2,2,2trifluoroethanol and activated aryl bromides at both higher (115 C) and lower temperatures (40 C). Unprecedentedly, this catalyst system facilitates the CeO cross-coupling reaction in short span of reaction times, generally 5e25 min (at 115 C). The structurally simple analogue of tBuXPhos ligand so called John-Phos (L2) ligand is also facilitated the CeO bond formation with activated aryl bromides and bromochalcones. Interestingly, under the optimal conditions (L1), methanol is also coupled rapidly with activated aryl bromides. These catalyst systems (L1 and L2) fail to couple electron rich aryl bromides with 2,2,2trifluoroethanol, thus these catalyst systems allow the reductive elimination through an electronic pathway of reductive elimination. The unusual reactivity of 2,2,2-trifluoroethanol in Pd-catalyzed CeO cross-coupling reaction makes that the chemistry of fluorinated molecules is unique than that of non-fluorinated analogues. The bromo-chalcones can be used as a new coupling partner in the cross-coupling reaction.
Trifluoroethanol: key solvent for palladium-catalyzed polymerization reactions
2005
A series of cationic palladium complexes of general formula [Pd(CH 3 )(NCCH 3 )(N-N)][X] (N-N = phen 1, 3-sec-butyl-1,10-phenanthroline (3-sBu-phen) 2, bpy 3, (À)-(S,S)-3,3 0 -(1,2-dimethylethylenedioxy)-2,2 0 -bipyridine (bbpy) 4, (+)-(R)-3,3 0 -(1-methylethylenedioxy)-2,2 0 -bipyridine (pbpy) 5, N,N 0 -bis(2,6-diisopropylphenyl)-2,3-butanediimine (iso-DAB) 6; X ¼ PF À 6 a, OTf (OTf = triflate) b) containing different nitrogen-donor ligands were prepared from the corresponding neutral chloro derivatives [Pd(CH 3 )(Cl)(N-N)] (1c-6c). They were characterized by 1 H NMR spectroscopy and elemental analysis. Single crystals suitable for X-ray determination were obtained for complexes [Pd(CH 3 )(NCCH 3 )(bbpy)][PF 6 ] (4a), [Pd(CH 3 )(NCCH 3 )(iso-DAB)][PF 6 ] (6a) and [Pd(Cl) 2 (bbpy)] (4c 0 ). The latter is the result of an exchange reaction of the methyl group, present in complex 4c, with a chloride, that occurred after dissolution of 4c in CDCl 3 , for 1 week at 0°C. The catalytic behavior of complexes 1a-5a and 1b-5b in the CO/styrene copolymerization was studied in CH 2 Cl 2 and 2,2,2-trifluoroethanol (TFE) evidencing the positive effect of the fluorinated alcohol both in terms of productivity and molecular weight values of the polymers obtained. Influence of the nitrogen ligand, the anion and the reaction time in both solvents were investigated and is discussed in detail. Encouraging preliminary results were also obtained in the synthesis of polyethylene, in TFE, catalyzed by [Pd(CH 3 )(NCCH 3 )(iso-DAB)][PF 6 ] (6a).
Journal of the American Chemical Society, 2015
A new biaryl monophosphine ligand (AlPhos, L1) allows for the room temperature Pd-catalyzed fluorination of a variety of activated (hetero)aryl triflates. Furthermore, aryl triflates and bromides that are prone to give mixtures of regioisomer-ic aryl fluorides with Pd-catalysis can now be converted to the desired aryl fluorides with high regioselectivity. Analysis of the solid-state structures of several Pd(II) complexes, as well as density functional theory (DFT) calculations, shed light on the origin of the enhanced reactivity observed with L1.
Journal of Fluorine Chemistry, 1996
Butane-1,4-diol was fluoroalkylated by its photoaddition reactions with hexafluoropropene and perfluoro (propyl vinyl) ether under atmospheric pressure, by which monofluoroalkylated and bis-fluoroalkylated products were obtained. 1,3-Diols were completely unreactive under the conditions. 2,2,2-Trifluoroethanol, tert.butyl alcohol and methyl tert.butyl ether appeared to be inert solvents for the additions while acetonitrile quenched the reactions. The reactivity of perfluoro vinyl ethers was studied (tested) in their photoaddition reactions with alkanols that were less regioselective (up to 7% rel.of regioisomer) in comparison with hexafluoropropene. Surprisingly, photo-supportedbase-induced nucleophilic mono-and bis-addition of butane-l+diol onto hexafluoroprnpene was observed in acetonitrile.