Stereochemistry of cyclic ether formation. Part I. Stereoselective intramolecular cyclisation of aliphatic disecondary 1,4-diols and their sulphonate esters to tetrahydrofurans

Abstract

Several methods of eliminative cyclisations of diastereoisomeric disecondary 1,4-diols and their 1,4-disulphonate esters, leading to the formation of tetrahydrofurans, have been studied, and it was found that they all proceed stereoselectively by S_N2-type mechanisms, with inversion of configuration at one (1,4-diols) or both (1,4-disul-phonates) chiral centres, so that meso(i.e. erythro) 1,4-diols and ±(i.e. threo) 1,4-dimesylates afford only trans-2,5-dialkyl-tetrahydrofurans, while the respective diastereoisomeric substrates are converted exclusively into cis-2,5-dialkyltetrahydrofurans.