Highly deoxygenated sugars.: I.: C2-branched glucose derivatives and carbon linked deoxygenated disaccharides

Triacetylglucal (1) is converted with high alpha-selectivity (>9:1) to the corresponding 2,3-unsaturated allyl and benzyl glycosides 2 and 3 using ferric chloride as the catalyst. The 6-O-silyl-protected allylic alcohol 5 is transformed to the 3,4-unsaturated C2-branched ester 6 or the amide 7 by Claisen rearrangement. The highly deoxygenated iodo lactone 8, resulting from the amide 6 by iodolactonization, is a versatile starting material for chiral building blocks 9-12. The 3,4-unsaturated C2-branched ester 6 is reduced to the aldehyde 14 and converted to a carbon linked disaccharide analogue 16 via cycloaddition with Danishefky's diene.