Véronique Blandin

Enhanced Spin-capturing Polymerization and Radical Coupling Mediated by Cyclic Nitrones

A series of cyclic nitrones have been tested for their spin-trapping activity in the enhanced spin-capturing polymerization of styrene and in nitrone-mediated radical coupling reactions. rac-2-Isopropyl-2,3-dimethyl-1-oxy-2,3-dihydro-imidazol-4-one was found to be the most efficient nitrone. The specific polystyrene macroradical addition rate to this nitrone was determined to be 8.0 × 103 L mol–1 s–1, which is by a factor of 10 higher than for previously studied compounds. Via enhanced spin-capturing polymerization, polymers in the range of oligomers to 30000 g mol–1 were obtained. A strong dependence of molecular weight on monomer conversion was observed, which can be explained by the high trapping rate. In nitrone-mediated radical coupling, almost ideal coupling of bromine-functional polymers was obtained and the successful introduction of the residual alkoxyamine functionality confirmed.

N-Hydroxy and N-acyloxy peptides: synthesis and chemical modifications

The preparation of a series of N-hydroxy peptides is described, along with their acylation on the oxygen of the pseudopeptide bond. Nineteen N-acyloxy peptides, first examples of this new class of pseudopeptides, were thus synthesized; they present a range of acyl groups, including N-protected amino acyl groups. Possibilities of elongation for these pseudopeptides were also investigated.

CHAPTER 3:Preparations and Applications of Hexyleneglycol Organoboronic Esters

The preparation and reactivity of hexylene-glycol boronic esters (2-alkyl-, 2-vinyl- or 2-aryl-4,4,6-trimethyl-1,3,2-dioxaborinanes) are reviewed, with particular consideration for comparison with other stable boronic esters derived from pinacol or neopentylglycol. Hexylene-glycol boronic esters are efficiently prepared by various methods (quenching of organometallics with trialkoxyboranes, hydroborations, metal-catalyzed C–X and C–H borylations), starting from storable, readily available reagents. The hexylene-glycol boronic esters are air, water, and chromatography stable, and readily soluble in organic solvents. They can be superior in reactivity to pinacol boronic esters. The chapter aims to demonstrate that expensive, sometimes sluggishly reacting pinacol boronic esters should often be replaced by other, less expensive, more reactive boronic esters such as their hexylene-glycol counterparts in the context of modern metal-catalyzed reactions.