Syntheses of optically active pentaacetates of pseudo-.BETA.-L-allopyranose and pseudo-.ALPHA.-D-mannopyranose.

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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.
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