Indium‐assisted allylation in carbohydrate chemistry: A convenient route to D‐glycero‐D‐galacto‐ and D‐glycero‐L‐galacto‐heptose

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Abstract
Starting with unprotected D‐pentoses 1–4 we achieved a chain elongation reaction by utilizing indium‐assisted allylation. After acetylation, the polyol derivatives 1a–4a were transformed into the corresponding α,β‐unsaturated aldehydes 1b–4b. Protection of the carbonyl group yielded the diethyl acetals 1c–4c. Subsequent dihydroxylation of the double bond by catalytic osmylation followed by acetylation of the newly introduced hydroxyl functions gave a mixture of diastereomeric products. However, only those diastereomers could be easily separated by column chromatography which were derived from 1c and 2c, giving access to D‐glycero‐D‐galacto and D‐glycero‐L‐galacto precursor 5 and 7, respectively. Final deprotection yielded the title aldoheptoses 6 and 8. magnified image