Jean Lessard

Hydrogen Evolution Reaction at Composite‐Coated Raney Nickel Electrodes in Aqueous and Aqueous‐Methanolic Solutions

The hydrogen evolution reaction was studied at composite-coated Raney nickel electrodes in aqueous and aqueous methanolic solutions containing 1M KOH at 25 o C, using ac impedance and steady-state polarization techniques. In aqueous solutions, the experimental results were analyzed by the constant-phase element (CPE) and the porous electrode models, and the resulting parameters were compared. In aqueous methanolic solutions it was found that the experimental data could be well approximated by both the fractal and the porous models. The kinetic parameters obtained in the different media were compared to those obtained on polycrystalline nickel

Photochemical Rearrangement of N-Chlorolactams: A Route to N-Heterocycles through Concerted Ring Contraction

We report a novel ring contraction allowing the direct conversion of N-chlorolactams to their corresponding ring-contraction N-heterocycles upon photolysis. Results show that the rearrangement occurs with a variety of N-chlorolactams and that the greater the substitution at the migrating carbon, the greater the yield of product. Importantly, stereochemistry at the migrating carbon is conserved in the product. Rearranged products were isolated as their methyl carbamates in yields varying from 17% to 58%, with the major side product being the recyclable parent lactam.

Converting cycloalkanones into N-heterocycles: formal synthesis of (-)-gephyrotoxin 287C.

The photochemical rearrangement of N-activated lactams enables their ring contraction concomitant with the migration of a carbon onto a nitrogen atom. When coupled with the Beckmann rearrangement, this photochemical ring contraction converts cycloalkanones into N-heterocycles in a few steps and in a stereospecific manner. To showcase the method, we performed an efficient formal synthesis of (-)-gephyrotoxin 287C.

Study of the Mechanism of the Hydrogen Evolution Reaction at Raney Nickel Electrodes in the Presence of Organic Compounds

The hydrogen evolution reaction (HER) has been studied at Raney nickel electrodes in the absence and presence of several organic compounds. A poisoning effect of nonreducible organic substrates on the kinetics of the HER was studied. It was found that only pyridine had a strong inhibiting effect on the HER. A compound having one reducible double bond, trans-cinnamic acid, was used as a model in a study of the mechanism of the electrocatalytic hydrogenation (ECH) reaction and its influence on the HER. It was established that the HER proceeds via the Volmer-Hyrovsky reaction mechanism, and the slowest step is the Heyrovsky reaction.

Photochemical rearrangement of N-mesyloxylactams: stereospecific formation of N-heterocycles.

N-Mesyloxylactams undergo an efficient ring-contraction to N-heterocycles of various ring sizes. Yields increase with the degree of substitution α to the carbonyl. The stereochemical information of a chiral migrating carbon is conserved making this reaction a synthetically useful complement to the well-known Hofmann, Curtius, Lossen, and Schmidt rearrangements.

The electrocatalytic hydrogenation of phenanthrene at Raney nickel electrodes: the influence of an inert gas pressure

The electrocatalytic hydrogenation (ECH) of phenanthrene (1) at Raney nickel electrodes in ethylene glycol-water (96:4 v/v) containing boric acid (0.1 M) and sodium chloride (0.1 M) has been investigated under medium pressure (from 3 to 41 atm) of an inert gas (nitrogen) at 80 and 110°C. Under steady current control (J=250 mA dm−2) at 80°C, pressures of 17–24 atm had an adverse effect on the efficiency of the reaction. Under periodic current control (J=625–700 mA dm−2 during t1=1 s and J=0 during t2=8 s) and under pressure (20.4 atm at 80°C, 41 atm at 110°C), the octahydrophenanthrenes (asymmetric (4) and symmetric (5)) were obtained in high yield (91%), conversion rate (99–100%) and current efficiency (94–96%) after a charge corresponding to 8 F mol−1. At 110°C and 41 atm, the yield of 4+5 reached 97% after 10 F mol−1 with 77% current efficiency.

Photochemical and thermal ring-contraction of cyclic hydroxamic acid derivatives.

Cyclic hydroxamic acids can undergo a thermal ring contraction after an in situ triflation. High yields of ring-contraction products are obtained with DBU when the migrating carbon is a methylene, while best results are obtained with Et(3)N for the migration of quaternary carbons. In some cases, the regiochemical outcome of the reaction can be controlled by changing the base. This novel thermal rearrangement complements a similar but photochemical rearrangement of N-mesyloxylactams.