Synthesis of Optically Active Pentaacetates of Pseudo-β-L-allopyranose and Pseudo-α-D-mannopyranose

Article abstract of DOI:10.1246/bcsj.60.2189

Diisobutylaluminium hydride reduction of D-glucose-derived chiral synthon, (1R,6R,8R,9R)-8,9-isopropylidenedioxy-7-oxabicyclo<4.3.0>non-4-en-3-one (1), gave a 7:1 mixture of (1R,3S,6R,8R,9R)- and (1R,3R,6R,8R,9R)-8,9-isopropylidenedioxy-7-oxabicyclo<4.3.0>non-4-en-3-ol, (2) and (2').Introduction of cis-diol to the double bond of 3-O-acetyl derivatives of 2 and 2' by osmium tetraoxide oxidation provided the diastereomeric mixture of (1R,3S,4R,5S,6S,8R,9R)-3-acetoxy-8,9-isopropylidenedioxy-7-oxabicyclo<4.3.0>nonane-4,5-diol (5) and (1R,3R,4S,5R,6S,8R,9R) diastereomer.Compound 5 was transformed to optically active pseudo-β-L-allopyranose effectively via (1R)-1-<(1S,2S,3S,4R,5S)-3,4,5-tris(benzyloxy)-2-hydroxycyclohexyl>-1,2-ethanediol (9).Cyclohexanecarbaldehyde formed by glycol cleavage of 9 was treated with methanesulfonyl chloride and reduced with lithium aluminium hydride to give (3S,4R,5S)-3,4,5-tris(benzyloxy)-1-cyclohexene-1-methanol (13).Compound 13 was efficiently converted to pseudo-α-D-mannopyranose pentaacetate by stereoselective hydroboration as a key reaction.The Wharton reaction of (1R,4S,5S,6S,8R,9R)-4,5-epoxy-8,9-isopropylidenedioxy-7-oxabicyclo<4.3.0>nonan-3-one derived from 1 gave (1R,5R,6S,8R,9R)-8,9-isopropylidenedioxy-7-oxabicyclo<4.3.0>non-3-en-5-ol, into which (3S,4S)-diol was stereoselectively introduced by oxidation with osmium tetraoxide.