Five enantiopure allylsilanes la-e have been prepared, with arabinose-derived alcohols methyl and benzyl 3,4-O-isopropylidene- and 3,4-O-methylene-β-L-arabinopyranosides as chiral auxiliaries, and subjected to the asymmetric Hosomi - Sakurai reaction. The effect of Lewis acid on the stereochemical outcome of the reaction was investigated, and BF3 was found to exhibit higher enantioselectivity than that of SnCl4 or TiCl4. The reaction of benzyl 2-O-(allyldimethylsilyl)-3,4-O-isopropylidene-β-L-arabinopyranoside (1b) with n-decanal gave the highest ee (45%) in the presence of BF3. The steric effect of the chiral auxiliary on the asymmetric Hosomi-Sakurai reaction is demonstrated for the first time although the stereogenic center is remote from the reaction site.
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