Sterospecific syntheses of marcrobicyclic polyethers with carbon bridgeheads from chiral glycerol derivatives

Abstract

The [3.3.3]cryptand (3), prepared stereospecifically from 2,3-O-isopropylidene-D-glycerol D-(1) and 2,3-di-O-benzyl-L-glycerol L-(2), has been separated chromatographically at –5 °C into slowly interconverting in-in ii-(3) and out-out oo-(3) conformational diastereoisomers [ΔG_ii→oo^‡=ca. 24 kcal mol^–1(1 kcal = 4.184 kj) in CD₃COCD₃ at +38 °C]; an X-ray structure analysis has shown (3) to from a crystalline 1 : 1 complex with Ba(SCN)₂ in which the Ba²⁺ ion is encapsulated by oo-(3) and the two SCN^– ion in an 11-co-ordinate manner.