Respective Contributions of Polar vs Enthalpy Effects in the Addition/Fragmentation of Mercaptobenzoxazole-Derived Thiyl Radicals and Analogues to Double Bonds

Synthesis of Sulfur-Substituted Bicyclo[1.1.1]pentanes by Iodo-Sulfenylation of [1.1.1]Propellane

Thiols easily react with [1.1.1]propellane to give sulfur-substituted bicyclo[1.1.1]pentanes in radical reactions, but this reactivity is not replicated in the case of heterocyclic thiols. Herein, we address this issue by electrophilically activating [1.1.1]propellane to promote its iodo-sulfenylation with 10 classes of heterocyclic thiols in two protocols that can be conducted on a multigram scale without exclusion of air or moisture.

Comparison of Thiyl, Alkoxyl, and Alkyl Radical Addition to Double Bonds: The Unusual Contrasting Behavior of Sulfur and Oxygen Radical Chemistry

High-level ab initio calculations have been used to compare prototypical thiyl, alkoxyl, and alkyl radical addition reactions. Thiyl radical addition to the sulfur center of thioketones is exothermic and rapid, occurring with negative enthalpic barriers and only weakly positive Gibbs free energy barriers. In stark contrast, alkoxyl radical addition to the oxygen center of ketones is highly endothermic and occurs with very high reaction barriers, though these are also suppressed. On the basis of analysis of the corresponding alkyl radical additions to these substrates and the corresponding reactions of these heteroatom radicals with alkenes, it suggested that addition reactions involving thiyl radicals have low intrinsic barriers because their unpaired electrons are better able to undergo stabilizing resonance interactions with the π* orbitals of the substrate in the transition state.

Tris(trimethylsilyl)silane (TTMSS)-Derived Radical Reactivity toward Alkenes: A Combined Quantum Mechanical and Laser Flash Photolysis Study

The reactivity of the tris(trimethylsilyl)silane (TTMSS)-derived radical is studied through an approach combining laser flash photolysis and quantum mechanical calculations. The results obtained for TTMSS are compared both to a classical silyl radical derived from triethylsilane and to a previously studied carbon-centered structure. Different worthwhile results are obtained: (i) the addition and hydrogen abstraction rate constants are directly measured, (ii) the high reactivity and the low selectivity of TTMSS toward the addition to alkenes are perfectly explained by antagonist polar and enthalpy effects, (iii) efficient hydrogen abstraction reactions from antioxidants such as vitamin E are observed, and (iv) TTMSS is seen to also act as an efficient initiator for the polymerization of an acrylate monomer.

Search for High Reactivity and Low Selectivity of Radicals toward Double Bonds: The Case of a Tetrazole-Derived Thiyl Radical

The search for new radical structures having both low selectivity and high reactivity toward the addition reaction onto alkenes can be of interest in organic synthesis or polymer chemistry and has led us to propose a new tetrazole-derived thiyl radical. The reactivity of this sulfur-centered structure is compared to that of an aminoalkyl radical also efficient for alkene addition Worthwhile results are obtained; the new structure is more reactive on the complete range of alkenes with addition rate constants higher than 107 M(-1) s(-1) for both electron-deficient (acrylonitrile, ...) or electron-rich (vinylether, ...) double bonds. Quantum mechanical calculations have allowed a better understanding of this unique feature.