Regioselectivity in alkylation reactions of 1,2-O-stannylene Acetals of D-arabinofuranose

The synthesis of beta-arabinofuranosides via alkylation of 1,2-O-stannylene aceta intermediates has been studied. With reactive alkyl halides (benzyl bromide, ally. bromide, and p-methoxybenzyl chloride), the method provides a mixture of R-arabinofuranosides and 2-O-alkylated lactols in ratios of 4:1 to 1:1.5. However, with carbohydrate-derived electrophiles, no alkylated products are produced. It appears, therefore, that the method is limited to the preparation of beta-arabinofuranosides of simple alcohols. Through the use of computational chemistry, we have explored the conformational properties of one of these stannylene acetals and propose that these: species exist in more than one conformation in solution and that this contributes to the: relatively poor regioselectivity in these reactions.