Radicals and Anions from Organohalides

Organic Synthesis Using Samarium Diiodide A Practical Guide By David J. Procter, Robert A. Flowers, II and Troels Skrydstrup David J. Procter, Robert A. Flowers, II, Troels Skrydstrup 2010 Published by the Royal Society of Chemistry, www.rsc.org 

Hexenyl radicals were used as radical clocks for the indirect measurement of the rate of reduction of radicals to anions using SmI2-HMPA. For example, reduction of primary iodide 4 using SmI2-HMPA resulted in the isolation of coupled product 9 in 20% yield and cyclised-coupled product 7 in 80% yield. As the rate of cyclisation of the intermediate primary hexenyl radical 6 was known, a rate constant of k= 106 M 1 s 1 could be estimated for the reduction 

The recognition of structural features in substrates that can potentially alter the course of reactions is important when planning reactions employing Sml2. 

---