The catalytic diastereo- and enantioselective Claisen rearrangement of 2-alkoxycarbonyl-substituted allyl vinyl ether

The catalytic asymmetric Claisen rearrangement of 2-alkoxycarbonyl-substituted allyl vinyl ethers that contain two stereogenic double bonds is described. A combination of the highly Lewis acidic [Cu[(S,S)-tert-Bu-box]](H2O)(2)(SbF6)(2) complex and molecular sieves served as catalyst and afforded the Claisen rearrangement products, substituted and functionalized alpha-keto esters, in high yield with a remarkable diastereo- and enantioselectivity. The influence of ligand structure, counterion and allyl vinyl ether double bond configuration on the stereoselectivity of the rearrangement was briefly investigated. We propose an explanation for the rate accelerating effect of the Lewis acid as well as a stereochermcal model which serve to explain and predict the stereochemical course of the copper bis(oxazoline) catalyzed Claisen rearrangement.