Patrick Diter

Experimental determination of the conformational free energies (A values) of fluorinated substituents in cyclohexane by dynamic 19F NMR spectroscopy. Part 2. Extension to fluoromethyl, difluoromethyl, pentafluoroethyl, trifluoromethylthio and trifluoromethoxy groups

The synthesis of monosubstituted and 1,4-substituted cyclohexanes bearing one of the title groups is described. The conformational analysis of these compounds was studied by 19F NMR spectroscopy at various temperatures. Chemical shifts for each conformer above the coalescence temperature were obtained by binomial regression from low temperature values, allowing the high precision determination of the equilibrium constants, and the corresponding thermodynamic parameters (ΔG°, ΔH°, ΔS°) of the fluorinated substituents. For A values (−ΔG°298K), the following averaged data were obtained: 1.59 (CFH2), 1.85 (CF2H), 2.67 (C2F5), 0.79 (OCF3) and 1.18 (SCF3) [in kcal mol−1].

Fluorinated Sulfilimino Iminiums: Efficient and Versatile Sources of Perfluoroalkyl Radicals under Photoredox Catalysis

Reported herein is the use of S-perfluoroalkyl sulfilimino iminiums as a new source of RF radicals under visible-light photoredox catalysis (RF =CF3 , C4 F9 , CF2 Br, CFCl2 ). These shelf-stable perfluoroalkyl reagents, readily prepared on gram scale from the corresponding sulfoxide using a one-pot procedure, allow the efficient photoredox-induced oxyperfluoroalkylation of various alkenes using fac-Ir(ppy)3 as the photocatalyst. Importantly, spin-trapping/electron paramagnetic resonance experiments were carried out to characterize all the radical intermediates involved in this radical/cationic process.

Radical allylation of trifluoromethylated xanthates: use of DEAD for removing the allyltributyltin excess

Abstract Radical allylation of trifluoromethylated xanthates allows the preparation of quaternary carbon centers bearing the trifluoromethyl group. An excess of the allyltributyltin reagent must be used in order to achieve satisfactory yields of the adducts. The excess of reagent could be conveniently removed by the use of diethylazodicarboxylate (DEAD).

Experimental determination of the conformational free energies (A values) of fluorinated substituents in cyclohexane by dynamic 19F NMR spectroscopy. Part 1. Description of the method for the trifluoromethyl group

The conformational free energy (A value) of the trifluoromethyl group was determined by variable temperature 19F NMR studies of trifluoromethylcyclohexanes bearing a substituent at the 4 position. 19F NMR chemical shifts for each conformer above the coalescence temperature were obtained by extrapolation from low temperature values, allowing the high precision determination of the equilibrium constants, and then the thermodynamic parameters (ΔG°, ΔH°, ΔS°). The validity of the hypothesis that substituent parameters are additive was discussed. Thermodynamic data of phenyl and cyclohexyl groups were also given.

Imidazolium-Based Ionic Liquids as Efficient Reagents for the C−O Bond Cleavage of Lignin

The demethylation of lignin in ionic liquids (ILs) was investigated by using pure lignin model monomers and dimers together with dioxane-isolated lignins from poplar, miscanthus, and maize. Different methylimidazolium ILs were compared and the samples were treated with two different heating processes: microwave irradiation and conventional heating in a sealed tube. The conversion yield and influence of the treatment on the lignin structure were assessed by 31 P NMR spectroscopy, size-exclusion chromatography, and thioacidolysis. The acidic methylimidazolium IL [HMIM]Br was shown to be an effective combination of solvent and reagent for the demethylation and depolymerization of lignin. The relatively mild reaction conditions, the clean work-up, and the ability to reuse the IL makes the described procedure an attractive and new green method for the conversion of lignin to produce phenol-rich lignin oligomers.

First isolation of enantiopure perfluoroalkylated sulfilimines and sulfoximines.

Mono-, di- and trifluoromethyl sulfilimines and sulfoximines have been isolated for the first time in enantiopure form by separation of the racemate by supercritical fluid chromatography. The electrophilic trifluoromethylating Shibata reagent has been prepared as a single enantiomer.

Dichlorotrifluoromethoxyacetic Acid: Preparation and Reactivity

We describe the first gram scale preparation of the reagent dichlorotrifluoromethoxyacetic acid. This stable compound is obtained in five steps starting from the cheap diethylene glycol. The reactivity of the sodium salt of this fluorinated acid was also tested and allowed the preparation of new amides.

One-Pot Synthesis of Aryl- and Alkyl S-Perfluoroalkylated NH-Sulfoximines from Sulfides

A general efficient one-pot synthesis of S-perfluoroalkylated NH-sulfoximines from sulfides has been developed using phenyliodine diacetate (PIDA) and ammonium carbamate. Remarkable rate enhancement with trifluoroethanol was observed, presumably due to H-bonding effects. These mild and metal-free conditions are compatible with -CH2 F, -CFCl2 , -CF2 H, -CF2 Br, -C4 F9 , and -CF3 groups, in both the alkyl- and aryl series. Based on a 19 F NMR analysis, a λ6 -acetoxysulfanenitrile intermediate was proposed.