Viridium: A Stable Radical and Its π-Dimerization.

The discovery of a stable organic radical formed under mild, clean, and efficient light-mediated conditions is reported. The structure of the stable acridinium-based radical photoproduct was unambiguously established by single-crystal X-ray diffraction, mass spectrometry, and in solution by EPR, UV/vis, and NMR spectroscopies. The photochemical mechanism of its formation has been elucidated by photophysical experiments coupled with EPR experiments and theoretical investigations.

Dual Photoredox Ni/Benzophenone Catalysis: A Study of the Ni Precatalyst Photoreduction Step.

The combination of NiX salts with a bipyridine-type ligand and aromatic carbonyl-based chromophores has emerged as a benchmark precatalytic system to efficiently conduct cross-couplings mediated by light. Mechanistic studies have led to two scenarios in which Ni is proposed as the catalytic species. Nonetheless, in none of these studies has a Ni to Ni photoreduction been evidenced.

Supramolecular Ladder Assemblies as a Model for Probing Electronic Interactions between Multiple Stacked π-Conjugated Systems.

A series of mono-, di-, and tri-topic receptors in which H-bonding sites, complementary to those of barbituric acid (BA), are fused is used to induce the supramolecular assembly of n×m ladders containing 1, 2, or 3 triphenylenevinylene units appended with BA. The topological constraint enforced by the architectures induces through-space interactions between the electroactive moieties that are reflected in the electronic absorption and emission spectrum. The n=2, m=2 or m=3 architectures undergo two single electron oxidation events, indicative of the formation of the corresponding mono- and di-radical cation species with comproportionation constants of 340 and 70, respectively.

A fluorous sodium l-prolinate derivative as low molecular weight gelator for perfluorocarbons.

We report the first study dealing with the self-assembly of an α-amino acid derivative in perfluorocarbons. Rheology, microscopy, and spectroscopy studies reveal that the fluorous sodium l-prolinate derivative 1 self-assembles in perfluorocarbons to form a three-dimensional network of left-handed nano-helices resulting in solvent gelation. Singlet oxygen lifetime measured in a gel of perfluorodecalin is about 1000 times longer than in pure water.

Thiourea-Catalyzed C-F Bond Activation: Amination of Benzylic Fluorides.

We describe the first thiourea-catalyzed C-F bond activation. The use of a thiourea catalyst and Ti(OiPr) as a fluoride scavenger allows the amination of benzylic fluorides to proceed in moderate to excellent yields. Preliminary results with S- and O-based nucleophiles are also presented.

Dual Benzophenone/Copper-Photocatalyzed Giese-Type Alkylation of C(sp )-H Bonds.

Photocatalyzed Giese-type alkylations of C(sp )-H bonds are very attractive reactions in the context of atom-economy in C-C bond formation. The main limitation of such reactions is that when using highly polymerizable olefin acceptors, such as unsubstituted acrylates, acrylonitrile, or methyl vinyl ketone, radical polymerization often becomes the dominant or exclusive reaction pathway. Herein, we report that the polymerization of such olefins is strongly limited or suppressed when combining the photocatalytic activity of benzophenone (BP) with a catalytic amount of Cu(OAc) .

Light-mediated iodoperfluoroalkylation of alkenes/alkynes catalyzed by chloride ions: role of halogen bonding.

An innovative procedure for the iodoperfluoroalkylation of alkenes/alkynes is described. These reactions, including iodotrifluoromethylations of alkenes, proceed very efficiently under low intensity UVA irradiation in deoxygenated methanol solutions containing catalytic amounts of NaCl or Bu4NCl. Preliminary mechanistic studies indicate that the light-promoted homolytic cleavage of the Rf-I bond that initiates the reaction is facilitated by the halogen bonding interaction between RfI and chloride ions.

Light-promoted metal-free cross dehydrogenative couplings on ethers mediated by NFSI: reactivity and mechanistic studies.

Cross dehydrogenative couplings on ethers occur very effectively using N-fluorobis(phenyl)sulfonimide (NFSI) as oxidizing agent under UVA irradiation in the presence of 2 mol% benzophenone. The reaction was shown to proceed first by fast radical fluorination of the α-C-H bond of ethers, followed by HF elimination to yield the highly electrophilic oxocarbenium ion as a key intermediate.

Organocatalyzed aldol reaction between pyridine-2-carbaldehydes and α-ketoacids: a straightforward route towards indolizidines and isotetronic acids.

Enantioselective aldol reactions between substituted pyridine carbaldehydes and α-ketoacids were shown to provide isotetronic acids or their corresponding pyridinium salts, depending on the nature of the substituents on the pyridine ring. The pyridinium salts were generated through nucleophilic attack of the pyridine nitrogen atom onto the reactive keto functional group. Moderate-to-good yields of both compounds were typically obtained and high levels of enantioselectivity were observed by using benzimidazole pyrrolidine I as a catalyst.