Ring closing metathesis and metal-catalyzed cyclopropanation for the preparation of sultone derivatives

Abstract

Ring closing metathesis (RCM) using Grubbs catalyst 2nd generation as a catalyst was applied to prepare series of novel unsaturated sultones with high yields. Many attempts, were applied for the cyclopropanation of the allylic sultones by Simmon-smith cyclopropanation using diethyl zinc/diiodomethane or Zn-Cu/diiodomethane but in each case the corresponding cyclic adduct was not formed. A novel palladium or preferably rhodium-catalyzed cyclopropanation of unsaturated sultones with ethyl diazoacetate was achieved by the transition metal-catalyzed transfer of a CH-CO2Et unit. The reaction was applied by a portion-wise addition of ethyl diazoacetate over 6h to a mixture of the sultones and palladium(II) acetate or rhodium(II) acetate dimer under low temperature (0-20 o C). The desired products of the cyclopropanation were achieved in each case, as a single diastereomer with 33- 37% yield in the allylic sultones and 10% for vinylic sultone.