On the diastereocontrol in the formation of (2R,3S)-3-(3′-furyl)-1,2-O-isopropylidenedioxy-3-pentanol and its (2R,3R)-diastereomer

The two enantiomeric bicyclic lactone skeletons of the marine natural products plakortones, whose absolute configuration are yet unknown, are approachable from (2R,3S)-3-(3′-furyl)-1,2-O-isopropylidenedioxy-3-pentanol 1a and its (2R,3R)-diastereomer 1b. To obtain these optically pure diastereomers, two pathways were studied, in which different solvents, additives and nucleophilic reagents were employed. The stereochemistry was successfully controlled in the reaction of (2R)-1,2-O-isopropylidenedioxy-3-pentanone 3 with 3-furyllithium, which gave high syn-selectivity in Et2O, but excellent anti-selectivity in toluene.