Smaller Substituents on Nitrogen Facilitate the Osmium-Catalyzed Asymmetric Aminohydroxylation

摘要

The β-hydroxyamino structural unit is a key motif in many biologically important molecules. It is difficult to imagine a more efficient means of creating this functionality than by direct addition of the two heteroatom substituents to an olefin, especially if this transformation could also be regio- and/or enan-tioselective when required. We recently reported the discovery of such a catalytic asymmetric aminohydroxylation (AA) reaction. On treatment with a chiral alkaloid ligand, catalytic osmium,Chloramine-T as the nitrogen source, and water as the oxygen source, olefins undergo enantioselective vicinal addition of a sulfonamido and a hydroxyl group. A limited range of substrates was investigated and enantioselectivities of up to 82% were achieved. These initial results clearly leave much room for improvement. Above all, higher enantioselectivities are needed and, when applicable, higher regioselectivities. Another goal is better chemoselectivity, which principally means suppressing formationofthe vicinal diol, sometimes a significant by-product.