Enantioselective Cyanosilylation of Ketones by a Catalytic Double-Activation Method with an Aluminium Complex and an N-Oxide

✍ Scribed by Fu-Xue Chen; Hui Zhou; Xiaohua Liu; Bo Qin; Xiaoming Feng; Guolin Zhang; Yaozhong Jiang

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 223 KB
• Volume: 10
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/chem.200400506

✦ Synopsis

Abstract

Double‐activation catalysis promises high catalytic efficiency in the enantioselective cyanosilylation of ketones through the combined use of a Lewis acid and a Lewis base. Catalyst systems composed of a chiral salen–Al complex and an N‐oxide have high catalytic turnovers (200 for aromatic ketones, 1000 for aliphatic ones). With these catalysts, a wide range of aliphatic and aromatic ketones were converted under mild conditions into tertiary cyanohydrin O‐TMS ethers in excellent yields and with high enantioselectivities (94 % ee for aromatic ketones, 90 % ee for aliphatic ones). Preliminary mechanistic studies revealed that the salen–Al complex played the role of a Lewis acid to activate the ketone and the N‐oxide that of a Lewis base to activate TMSCN; that is, double activation.