Reaction of Phenyl-Substituted Allyllithiums with tert-Alkyl Bromides. Remarkable Difference in the Alkylation Regiochemistry between a Polar Process and the One Involving Single-Electron Transfer

Article abstract of DOI:10.1021/ja00245a033

The reaction of phenyl-substituted allyllithiums 1a-h with tert-alkyl bromides was investigated systematically.The alkylation regiochemistry was influenced in a complicated fashion by various factors including substituent effects, both steric and electronic, solvents, and the presence of strongly coordinating additives, tetramethylethylenediamine and hexamethylphosphoramide.On the basis of the cyclizable probe experiments, the observed regiochemistry was interpreted as follows. (a) The reaction proceeds by two alternative pathways, a polar one and single electron transfer (SET), the extent of each path being influenced by the variable factors and (b) a polar pathway favors coupling at the phenyl-substituted site (C-1), while in the case of SET the C-C bond formation occurs predominantly at the site far from the phenyl substituent (C-3).