A new series of catalysts is able to selectively make “left-handed” or “right-handed” nitrogen-containing compounds known as amines. Left-handed and right-handed molecules contain the same components, but are mirror images of each other. Researchers were able to take strings of nitrogen-containing molecules and make five-, six- and seven-membered rings with enantiomeric excess of 90%. Most other catalysts produce a mixture of both enantiomers. Researchers studied hafnium, titanium and zirconium (Group 4) containing catalysts and found the zirconium catalysts to be the best at producing one enantiomer in high yield over the other. The new zirconium catalysts do what no other Group 4 catalyst has done before — they can operate at room temperature and down to minus 20 °F. All other zirconium catalysts operate at 300 °F. These new catalysts are also tolerant of various functional groups attached to the amines. Researchers performed detailed studies of the structure, activity and selectivity of this system of catalysts and were able to characterize the reaction pathways. The pursuit of these optically active amines is important for improved syntheses of commodity and specialty chemicals.
Highly Enantioselective Zirconium-Catalyzed Cyclization of Aminoalkenes