Intramolecular homolytic substitution in selenoxides and selenones

G3(MP2)-RAD calculations provide activation energies for intramolecular homolytic substitution in the 4-(alkylselenoxo)butyl and 4-(alkylselendioxo)butyl radicals ranging from 21–39 kJ mol−1, and 143–170 kJ mol−1 for the selenoxide and selenone, respectively. Arrhenius data translate into rate constants for ring-closure of 1.5×105−2.5×108 s−1 (80°) for the selenoxides, and 5.4×10−14−5.1×10−11 s−1 (80°) for the corresponding selenones. NBO analyses show alkyl radicals are electrophilic during homolytic substitution at selenoxide selenium. The dominant orbital interaction in the transition state is worth 2413 kJ mol−1 and involves the SOMO and the lone-pair of electrons on selenium. The corresponding selenones are calculated to ring-close through transition states in which alkyl radicals are nucleophilic, but involve weak (SOMO--> σ* and SOMO--> π*) interactions. Consequently, this chemistry is not viable for selenones because of the lack of lone-pairs of electrons on the chalcogen

7-Selenabicyclo2.2.1heptane

Thermolysis of a benzene solution of N-4-(p-(methoxybenzyl)seleno) cyclohexanoyl-N,S-dimethyldithiocarbonate affords the hitherto unknown 7-selenabicyclo2.2.1heptane in 48% conversion and in 20% yield after chromatography. G3(MP2)-RAD calculations predict a rate constant of 5 X 104 s-1 at 80 °C (3.8 X 106 s -1 at 200 °C) for the intramolecular homolytic substitution process involved in this cyclization

Preparation of Novel Selenopenams by Intramolecular Homolytic Substitution

Abstract: Photolyses of the thiohydroximate ester derivatives 13 and 21 of the 4-(benzyl-seleno)-2-azetidinoines 7 and 20, afford the 1-aza-7-oxo-4-selenabicyclo-[3.2.0]heptane ring systems 14 and 21 in good to moderate yield in processes that presumably involve intramolecular homolytic substitution at selenium with expulsion of benzyl radical. Extension of this methodology to the preparation of derivatives 24 of 12,2a-dihydro-1H,8H-azeto[2,1-b][1,3]benzoselenazin-1-one (22) is also described

Intramolecular homolytic substitutions in synthesis

Free radical chemistry contributes to the modern chemists’ toolbox in ways that were unimaginable only a few decades ago. There can be no doubt that the construction of carbocyclic and heterocyclic ring systems through the intramolecular addition of alkyl, aryl, and other radicals to unsaturated functionalities is a major contribution to synthetic methodology; this chemistry is the topic of other contributions to this collective work

Toward Pyridine-Fused Selenium-Containing Antioxidants

Abstract: Photolysis of the thiohydroximate ester derivative 21 of 2-carboethoxy-2-(2-(benzylseleno)pyridin-3-yl)tridecylcarboxylic acid (20) affords 2-dodecyl-2carboethoxy-2,3-dihydroselenolo[2,3-b]pyridine (22) in 89 % yield in a process presumably involving intramolecular homolytic substitution by a tertiary alkyl radical at selenium with loss of a benzyl radical. Work toward extending this methodology to the preparation of pyridine-fused selenium analogues of antioxidants is described

Thiols, thioethers, and related compounds as sources of C-centred radicals

Due to their stability, availability and reactivity, sulfides are particularly attractive sources of carbon-centered radicals. However, their reactivity in homolytic substitution processes is strongly reduced when compared with the corresponding selenides or halides. Despite this, sulfur-containing compounds can be engineered so that they become effective agents in radical chain reactions. A detailed description of the reactivity of organo-sulfur compounds is reported here with the aim of providing clear guidance on the scope and limitation of their use as radical precursors in chain reactions