Efficient bimetallic titanium catalyst for carbonyl-ene reaction

✍ Scribed by Fang Fang; Fang Xie; Han Yu; Hui Zhang; Bo Yang; Wanbin Zhang

• Publisher: Elsevier Science
• Year: 2009
• Tongue: French
• Weight: 498 KB
• Volume: 50
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/j.tetlet.2009.09.078

✦ Synopsis

A new family of achiral 3,3 0 ,5,5 0 -tetrasubstituted-2,2 0 ,6,6 0 -tetrahydroxy biphenyl ligand 4 was developed. The axial chirality of the ligand could be induced by the chelation of 2,2 0 ,6,6 0 -tetrahydroxy groups with (R)-BINOL-Ti(O i Pr) 2 to form an axially chiral bimetallic titanium catalyst 9. Compared with (R)-BINOL-Ti(O i Pr) 2 catalyst, this novel catalyst 9 exhibited excellent activity and enantioselectivity for the carbonyl-ene reaction of methylstyrene and ethyl glyoxylate. 3,3 0 ,5,5 0 -Tetrasubstituted groups showed a remarkable effect on both enantioselectivity and yield. With 9d prepared from 3,3 0 ,5,5 0 -tetramethyl-2,2 0 ,6,6 0 -tetrahydroxy biphenyl 4d as the catalyst, the best result, up to 97.6% ee and 99% yield, was obtained. Additionally, the bimetallic catalyst 9 also showed better catalytic capability than the corresponding monometallic catalyst.