Use of a conformational radical clock for evaluating alkyllithium-mediatedcyclization reactions

[GRAPHICS] The reductive lithiation of nitrile 9 led to the cyclic product 11 as a sin gle diastereomer in 42% ee, The intermediate radical is a conformational ra dical clock. The radical lifetime can be determined from the optical purity of the product 11, We show that the lifetime of the intermediate radical i s too brief to allow a radical cyclization, and thus the cyclization procee ds through an alkyllithium intermediate.