SYNTHESIS OF SOME OUT,IN-MACROBICYCLIC AND OUT,OUT-MACROBICYCLIC POLYETHERS DERIVED FROM GLYCEROL - OUT,IN-IN,OUT ISOMERISM

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 outjn-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 outin-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.