Beilstein J. Org. Chem.2006,2, No. 10, doi:10.1186/1860-5397-2-10
us to suggest that some radicals in the Wille cascade progress to products by oxidation or group transfer rather than β-fragmentation.
Results and Discussion
We choose to generate the candidate radicals for fragmentation by a radicalcyclization rather than by a standard atom or group abstraction
radicalcyclization of enol ether 11a with tributyltin hydride (0.1 M) followed by chromatographic purification provided 14a in 95% yield as an inseparable 1:2 mixture of exo and endo isomers. Likewise, cyclization of enol ester 11b provided a 1:2 mixture of 14b-exo and 14b-endo in 68% isolated yield. The
concentrations, complete conversion of 11b was observed and reduced product 14b was formed in good yield. None of the directly reduced product 18b was observed even at the highest concentration, indicating that the intermediate radicalcyclization is fast (kC > 106 s-1). Negligible amounts of ketone 15 (≤ 2