Alkylation of Allylic Derivatives. On the Regio- and Stereochemistry of Alkylation of Allylic Alcohols by the Murahashi Method

Article abstract of DOI:10.1021/jo00323a034

Direct alkylation of allylic alcohols by the Murahashi method has been reinvestigated.This four-step, one-pot process evidently involves formation of the lithium (allyloxy)alkylcuprate (2) followed by the reaction with (methylphenylamino)triphenylphosphonium iodide (1a) or the corresponding tributylphosphonium iodide (1b).Contrary to earlier implications, the regiospecific and stereospecific anti γ-alkylation is independent of which aminophosphonium reagent is used.Presumably the final step involves alkylation of the (allyloxy)phosphonium ion (3) by LiCu(R)(N(CH3)Ph).This mixed cuprate also alkylates allylic carboxylates with about the same regio- and stereochemistry as for the Murahashi direct alkylation of the corresponding allylic alcohol.A general mechanism is presented that suggests that the regiochemistry of alkylation of allylic derivatives depends on the nature of the ancillary ligand in the alkylating cuprate.