Sara H. Kyne

First determination of the rate constant for ring-closure of an azahexenoyl radical: 6-aza-7-ethyl-5-hexenoyl

Competitive kinetic experiments utilising free radical carbonylation chemistry provide a first estimate for the rate constant for 6-endo cyclization of the 6-aza-7-ethyl-5-hexenoyl radical of (4.8 +/- 2.4) x 10(6) s(-1) at 90 degrees C in benzene, in good agreement with ONIOM-G3(MP2)-CC+COSMO-RS calculations (6.8 x 10(6) s(-1)).

Multi-component orbital interactions during oxyacyl radical addition reactions involving imines and electron-rich olefins

Ab initio and DFT calculations reveal that oxyacyl radicals add to imines and electron-rich olefins through simultaneous SOMO-pi*, SOMO-pi and pi*-HOMO interactions between the radical and the radicalophile. At the BHandHLYP/aug-cc-pVDZ level, energy barriers of 20.3 and 22.0 kJ mol(-1) are calculated for the attack of methoxycarbonyl radical at the carbon and nitrogen ends of methanimine, respectively. In comparison, barriers of 22.0 and 8.6 kJ mol(-1) are calculated at BHandHLYP/aug-cc-pVDZ for reaction of methoxycarbonyl radical at the 1- and 2-positions in aminoethylene, respectively. Natural bond orbital (NBO) analysis at the BHandHLYP/6-311G** level of theory reveals that SOMO-pi*, SOMO-pi and pi*-LP interactions are worth 111, 394 and 55 kJ mol(-1) respectively in the transition state (8) for reaction of oxyacyl radical at the nitrogen end of methanimine; similar interactions are observed for the chemistry involving aminoethylene. These multi-component interactions are responsible for the unusual motion vectors associated with the transition states involved in these reactions.

Executing and rationalizing the synthesis of a difluorinated analogue of a ring-expanded calystegine B2.

A difluorinated analogue of a ring-expanded calystegine B(2) and some N-protected species were prepared via microwave-mediated transannular ring-opening of an epoxyketone. The diastereofacial selectivity of the epoxidation reaction, which delivers the key intermediate, and the regioselectivity of the transannular reactions were analyzed by density functional theory (DFT) methods. The epoxidation stereoselectivity arises from simple steric control, whereas the ring-closure reactions are subject to thermodynamic control.

Ab Initio Studies of Carbonyl Radical Additions to Hydrazone Systems

Ab initio and DFT calculations reveal that intermolecular radical additions of both acyl and oxyacyl radials to hydrazones occur through SOMO → π*hydrazone, πhydrazone → SOMO and LPN → SOMO interactions between the radical and the hydrazone π-system. Both acetyl and methoxycarbonyl radicals show preference for addition to the carbon end of the carbon–nitrogen π-bond. At the highest level of theory used in this study (G2//MP2(full)/6-31G*), energy barriers of 11.2 and 22.6 kJ mol–1 are calculated for acetyl radical addition to the carbon and nitrogen-ends of N-aminomethanimine respectively. The analogous energy barriers for the methoxycarbonyl radical are 4.9 and 25.7 kJ mol–1 at the same level of theory.

Organometallic catalysis for applications in radical chemistry and asymmetric synthesis

Abstract Two organometallic catalysis studies are presented. The first one deals with the development of a new catalytic agent based on the mixture of a hydride and an iron salt to trigger efficient radical cyclization processes. In a second line of research, we have shown that the use of chiral anions can outperform chiral ligands in a carbocyclization reaction and a [2 + 2 + 2] cycloaddition.

Homolytic substitution chemistry: from James Franz to antihypertensives

There was a time when free radicals were scorned by organic chemists and when “practically every organic text book written” contained a statement that free radicals were “incapable of an independent existence”.