Jean-François Paquin

Fluorine Transfer to Alkyl Radicals

The development of new synthetic technologies for the selective fluorination of organic compounds has increased with the escalating importance of fluorine-containing pharmaceuticals. Traditional methods potentially applicable to drug synthesis rely on the use of ionic forms of fluorine (F(-) or F(+)). Radical methods, while potentially attractive as a complementary approach, are hindered by a paucity of safe sources of atomic fluorine (F(•)). A new approach to alkyl fluorination has been developed that utilizes the reagent N-fluorobenzenesulfonimide as a fluorine transfer agent to alkyl radicals. This approach is successful for a broad range of alkyl radicals, including primary, secondary, tertiary, benzylic, and heteroatom-stabilized radicals. Furthermore, calculations reveal that fluorine-containing ionic reagents are likely candidates for further expansion of this approach to polar reaction media. The use of these reagents in alkyl radical fluorination has the potential to enable powerful new transformations that otherwise would take multiple synthetic steps.

Direct C–F Bond Formation Using Photoredox Catalysis

We have developed the first example of a photoredox catalytic method for the formation of carbon-fluorine (C-F) bonds. The mechanism has been studied using transient absorption spectroscopy and involves a key single-electron transfer from the (3)MLCT (triplet metal-to-ligand charge transfer) state of Ru(bpy)3(2+) to Selectfluor. Not only does this represent a new reaction for photoredox catalysis, but the mild reaction conditions and use of visible light also make it a practical improvement over previously developed UV-mediated decarboxylative fluorinations.

Friedel–Crafts Reaction of Benzyl Fluorides: Selective Activation of CF Bonds as Enabled by Hydrogen Bonding

A Friedel-Crafts benzylation of arenes with benzyl fluorides has been developed. The reaction produces 1,1-diaryl alkanes in good yield under mild conditions without the need for a transition metal or a strong Lewis acid. A mechanism involving activation of the C-F bond through hydrogen bonding is proposed. This mode of activation enables the selective reaction of benzylic C-F bonds in the presence of other benzylic leaving groups.

Enabling Nucleophilic Substitution Reactions of Activated Alkyl Fluorides through Hydrogen Bonding

It was discovered that the presence of water as a cosolvent enables the reaction of activated alkyl fluorides for bimolecular nucleophilic substitution reactions. DFT calculations show that activation proceeds through stabilization of the transition structure by a stronger F···H2O interaction and diminishing C-F bond elongation, and not simple transition state electrostatic stabilization. Overall, the findings put forward a distinct strategy for C-F bond activation through H-bonding.

Design, Synthesis, and Applications of Potential Substitutes of t-Bu-Phosphinooxazoline in Pd-Catalyzed Asymmetric Transformations and Their Use for the Improvement of the Enantioselectivity in the Pd-Catalyzed Allylation Reaction of Fluorinated Allyl Enol Carbonates

The design, synthesis, and applications of potential substitutes of t-Bu-PHOX in asymmetric catalysis is reported. The design relies on the incorporation of geminal substituents at C5 in combination with a substituent at C4 other than t-butyl (i-Pr, i-Bu, or s-Bu). Most of these new members of the PHOX ligand family behave similarly in terms of stereoinduction to t-Bu-PHOX in three palladium-catalyzed asymmetric transformations. Electronically modified ligands were also prepared and used to improve the enantioselectivity in the Pd-catalyzed allylation reaction of fluorinated allyl enol carbonates.

Halogenation of Primary Alcohols Using a Tetraethylammonium Halide/[Et2NSF2]BF4 Combination

The halogenation of primary alcohols is presented. The use of a combination of tetraethylammonium halide and [Et(2)NSF(2)]BF(4) (XtalFluor-E) allows for chlorination and bromination reactions to proceed efficiently (up to 92% yield) with a wide range of alcohols. Iodination reactions are also possible albeit in lower yields.

Synthesis and growth inhibition activity of fluorinated derivatives of tamoxifen

The design and synthesis of 11 fluorinated derivatives of tamoxifen are described. Growth inhibition values (GI50) on human HT-29, M21, MCF7, and MDA-MB-231 tumor cells are also reported. In general, the GI50 values are similar or slightly higher than tamoxifen with the most active compound on MCF7 cell line having a GI50=3.6μM. Surprisingly, as opposed to tamoxifen, both geometrical isomers behave similarly. We hypothesize that this behavior is due to in vitro isomerization of the compounds.

Introduction of the 4,4,4-trifluorobut-2-ene chain exploiting a regioselective Tsuji-Trost reaction catalyzed by palladium nanoparticles.

A palladium-nanoparticle-catalyzed Tsuji-Trost reaction of 4,4,4-trifluorobut-2-en-1-yl acetate and ethyl(4,4,4-trifluorobut-2-en-1-yl)carbonate was accomplished with various nucleophiles including phenols, amines, and malonates. In the case of the phenols, isomerization of the double bond in the product (up to 20%) was observed as a side reaction. Further synthetic transformations including hydrogenation, the Diels-Alder reaction, and asymmetric dihydroxylation of a product were also examined.

Quinazoline-4-piperidine sulfamides are specific inhibitors of human NPP1 and prevent pathological mineralization of valve interstitial cells

Ectonucleotide pyrophosphatase/PDE1 (NPP1) is an ectoenzyme, which plays a role in several disorders including calcific aortic valve disease (CAVD). So far, compounds that have been developed as inhibitors of NPP1 lack potency and specificity. Quinazoline‐4‐piperidine sulfamides (QPS) have been described as potent inhibitors of NPP1. However, their mode of inhibition as well as their selectivity and capacity to modify biological processes have not been investigated.

Triol-promoted activation of C–F bonds: Amination of benzylic fluorides under highly concentrated conditions mediated by 1,1,1-tris(hydroxymethyl)propane

Summary Activation of the C–F bond of benzylic fluorides was achieved using 1,1,1-tris(hydroxymethyl)propane (2) as a hydrogen bond-donating agent. Investigations demonstrated that hydrogen bond-donating solvents are promoting the activation and hydrogen bond-accepting ones are hindering it. However, the reaction is best run under highly concentrated conditions, where solvents cannot interfere with the interaction between the organofluorine compound and the triol. Various benzylic fluorides react with secondary amines or anilines to form benzylic amines in good yields.