The Trisaccharide Model

4-diol 456 (84% from 454). Treatment of 456 with dibutyltin oxide in toluene afforded the stannylidene acetal, which was reacted with ethyl bromoacetate in the presence of tetrabutylammonium iodide to give the ether lactone 457 in 82% yield. The 4-methoxybenzyl ether protecting group was removed from 457 by the action of 2,3-dichloro-5,6-dicyano-l,4-benzoqumone (DDQ 458,88%). Alcohol 

458 was glycosylated under Nicolaou s conditions of the Mukaiyama glycosylation reaction (silver perchlorate, tin(II) chloride in dichloromethane-ether) using as fucosyl donor the benzylated fluoride 170. Donor 170 had been obtained in 85% yield by treating the known 2,3,4-tri-O-benzyl-L-fucopyranosc with diethy-laminosulfur trifluoride (DAST). The desired -D-Gal-a-L-Fuc diastereoisomer 

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