The effect of crown ether on steric hindrance to base approach in bimolecular elimination: evidence against clump aggregate model of ion-paired alkoxide base

Abstract

The effect of 18-crown-6-ether upon geometrical orientation and rates was investigated in tert-C4H9OK-tert-C4H9OH promoted anti-elimination from two homologous series of tosylates, RCH2CHOTsC5H11 and RCHOTsCH2C5H11 (R = H, CH3, C2H5, n-C3H5, iso-C3H7, tert-C4H9). Steric requirements of the cis- and trans-stereoselective base species operating in the reaction in the absence and in the presence of the crown ether, respectively, have been assessed. An unambiguous distinction has been made between two pending models of the cis-stereoselective (ion-paired) base.