Use of a conformational radical clock for evaluating alkyllithium-mediated cyclization reactions.

The reductive lithiation of nitrile 9 led to the cyclic product 11 as a single diastereomer in 42% ee. The intermediate radical is a conformational radical clock. The radical lifetime can be determined from the optical purity of the product 11. We show that the lifetime of the intermediate radical is too brief to allow a radical cyclization, and thus the cyclization proceeds through an alkyllithium intermediate.