DESIGN, SYNTHESIS, AND APPLICATIONS OF NEW OXYGENATED CHIRAL AUXILIARIES

The magnesium bromide etherate-mediated addition of allyltributyltin to an alpha-alkoxyaldehyde bearing a protected 3-hydroxytetrahydropyranyl- moiety was shown to be highly diastercoselective. The sense and the level of induction depend on the nature of the protecting group at C-3. Esters and benzyl ether gave the opposite relative stereochemistry in comparison to silyl ethers. It was also found that the other enantiomer of an optically active 1,2-diol could be obtained using the same chiral auxiliary simply by changing the stereochemistry at the anomeric position. The exceptionally high level of 1,4-induction in these systems was attributed to the formation of a tridentate chelate involving one oxygen atom of the auxiliary and both oxygen atoms of the aglycone.