Synthesis of some out,in- and out,out-macrobicyclic polyethers derived from glycerol. Out,in–in,out isomerism

Abstract

Macrobicyclic polyethers containing carbon bridgeheads have been synthesised from achiral and chiral glycerol derivatives. Syntheses based on cis-1,3-O-benzylideneglycerol yield a mixture of out,out- and out, in-isomers of these macrobicyclic compounds, whereas syntheses based upon 2,3-O-isopropylidene-D-glycerol afford stereospecific routes to the out,in-isomers. ¹³C N.m.r. spectroscopy indicates that the out,in-macrobicyclic polyethers are undergoing out,in–in,out isomerization, and in two compounds the interconversion is slowed sufficiently on cooling for separate bridgehead carbon resonances to be observed. A rationalization is presented for the relative conformational mobility observed in the series of out,in-compounds studied. Added potassium ions produce significant changes in the ¹³C n.m.r. spectra of certain of the macrobicyclic polyethers, and it is suggested that these changes are a result of complexation of the cation by the bicyclic compound.