The copper-catalyzed asymmetric addition of 2-silyloxyfurans to cyclic unsaturated oxo esters is reported. The reaction proceeds with excellent diastereocontrol (usually dr 99:1) and modest to high enantioselectivity, depending on the nature of the ester group and the substitution of the cyclic oxo ester. We have shown that these substrates can be transformed into a variety of building blocks bearing a gamma-butenolide or gamma-lactone connected to a cycloalkane or cycoalkene moiety.
Vinylogous Mukaiyama-Michael Reactions between 2-Silyloxyfurans and Cyclic Enones or Unsaturated Oxo Esters
Lewis acid catalyzed vinylogous Mukaiyama–Michael (VMM) reactions between 2-(trialkylsilyloxy)furans 1 and α,β-unsaturatedcyclic enones 2 or oxo esters 4 have been investigated. Both substrates proved to be useful Michael acceptors in the title reaction, giving the butenolides 3 and 5 in good yields. A comparative study between the α,β-unsaturatedcyclic enones 2 and the oxo esters 4 as Michael acceptors