Eric Besson

Mechanistic Investigation of Enediyne-Connected Amino Ester Rearrangement. Theoretical Rationale for the Exclusive Preference for 1,6- or 1,5-Hydrogen Atom Transfer Depending on the Substrate. A Potential Route to Chiral Naphthoazepines

Memory of chirality (MOC) and deuterium-labeling studies were used to demonstrate that the cascade rearrangement of enediyne-connected amino esters 1a and 1b evolved through exclusive 1,5- or 1,6-hydrogen atom transfer, subsequent to 1,3-proton shift and Saito-Myers cyclization, depending on the structure of the starting material. These results were independently confirmed by DFT theoretical calculations performed on model monoradicals. These calculations clearly demonstrate that in the alanine series, 1,5-hydrogen shift is kinetically favored over 1,6-hydrogen shift because of its greater exergonicity. In the valine series, the bulk of the substituent at the nitrogen atom has a major influence on the fate of the reaction. N-Tosylation increases the barrier to 1,5-hydrogen shift to the benefit of 1,6-hydrogen shift. The ready availability of 1,6-hydrogen atom transfer was explored as a potential route for the enantioselective synthesis of naphthoazepines.

Arylsulfanyl radical lifetime in nanostructured silica: dramatic effect of the organic monolayer structure

Nanostructured hybrid silicas, in which covalently anchored aromatic thiols are regularly distributed over the pores, enable a dramatic increase in the half-lives of the corresponding arylsulfanyl radicals. This enhancement is not only due to limited diffusion but also to the structure of the organic monolayer on the surface of the pores. Molecular dynamics modeling shows that at high loadings, in spite of their spatial vicinity, supramolecular interactions disfavor the coupling of arylsulfanyl radicals. As compared to phenylsulfanyl radical in solution, the half-life measured at 293 K can be increased by 9 orders of magnitude to reach 65 h.

Investigating Unusual Organic Functional Groups to Engineer the Surface Chemistry of Mesoporous Silica to Tune CO2–Surface Interactions

As the search for functionalized materials for CO2 capture continues, the role of theoretical chemistry is becoming more and more central. In this work, a strategy is proposed where ab initio calculations are compared and validated by adsorption microcalorimetry experiments for a series of, so far unexplored, functionalized SBA-15 silicas with different spacers (aryl, alkyl) and terminal functions (N3, NO2). This validation then permitted to propose the use of a nitro-indole surface functionality. After synthesis of such a material the predictions were confirmed by experiment. This confirms that it is possible to fine-tune CO2-functional interactions at energies much lower than those observed with amine species.

Evidence for the contribution of degenerate hydrogen atom transport to the persistence of sulfanyl radicals anchored to nanostructured hybrid materials

Nanostructured functionalized silicas were used as a platform to compare the behaviour of anchored arylsulfanyl radicals depending on the nature of the precursor (diazene/thiol). The radicals generated from thiols exhibit higher half-lifetimes than the radicals generated from diazenes. The ability of thiols to maintain the sulfanyl radical density via degenerate hydrogen atom transfer is likely to account for this sharp difference.