Catalytic enantioselective allylic oxidation of olefins

Abstract

Asymmetric version of allylic oxidation of oletins to a1lylic esters is an important transformation, The reaction is performed usually using peresters in the presence of a metal catalyst in a chiral environment. Copper catalyst was mainly used by most of the people. Development in this area has been summarized here in a chronological manner. Initially, a modest asymmetric induction in this reaction was achieved by using a variety of chiraI amino acids. Lately, a variety of chiral ligands have been introduced to obtain high enantiomeric excess (up to 93% ee) in the allylic oxidation of a variety of cyclic oletins. One of the drawbacks of the reaction was longer time ranging from a week to a month for completion. This shortcoming was overcome to some extent by using phenylhydrazineJphenylhydrazone in the reaction mixture. The reason for enhancement in rate of the reaction is not yet clear, but the reaction can now be completed within a day or two without loosing enantioselectivity. Despite so much progress in this area, the reaction is restricted only to cyclic oletins. Acyclic oletins do not give high asymmetric induction.