On the Reduction of Tertiary Radicals by Samarium Diiodide (SmI2)

Reduction of o-iodophenyl 3-methylbut-2-enyl ether with samarium diiodide generates mixtures of 3-isopropyl-2,3-dihydrobenzofuran and 3-(2-propenyl)-2,3-dihydrobenzofuran along with a small amount of dimer. If a source of deuterium is present during the reduction, then the 3-isopropyl product predominates and this product is labeled with one deuterium. However, attempts to quench the putative tertiary organosamarium reagent by adding a deuterium source after the reduction were not very successful at room temperature. But at 0°C, the organosamarium reagent was generated (at least to the extent of about 50%, as measured by deuterium quenching), and its decomposition was followed over time by a series of quenching experiments. The results suggest that tertiary radicals are reduced to a significant extent by SmI2 to form an anionic (presumably alkylsamarium) species. This species is thermally unstable and decomposes to the corresponding reduced and eliminated products. The reduced product is consistently formed in slight excess over the eliminated one, and the mechanism of formation of these products is not yet clear