Asymmetric Aerobic Oxidation of -Hydroxy Acid Derivatives by C4-Symmetric, Vanadate-Centered, Tetrakisvanadyl(V) Clusters Derived from N-Salicylidene--aminocarboxylates

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• 作者：Chien-Tien Chen ; Sampada Bettigeri ; Shiue-Shien Weng ; Vijay D. Pawar ; Ya-Hui Lin ; Cheng-Yuan Liu ; Way-Zen Lee
• 刊名：Journal of Organic Chemistry
• 出版年：2007
• 出版时间：October 26, 2007
• 年：2007
• 卷：72
• 期：22
• 页码：8175 - 8185
• 全文大小：654K
• 年卷期：v.72,no.22(October 26, 2007)
• ISSN：1520-6904

文摘

D=jo070575fn00002>A series of chiral vanadyl(V) methoxides bearing 3-t-butyl-5-substituted N-salicylene-L-valinate and L-t-leucinate as chiral auxiliaries has been prepared. In all cases except the 3,5-di-t-butyl analogue, theyexist as monomers both in solution and in the single crystal state. In the case of the 3,5-di-t-butyl analogue,the architectural nature of the vanadyl(V) complex highly depends on the base used during the complexformation event. A pentanuclear C₄-symmetric complex was formed when potassium salts were employedinstead of the corresponding sodium salts. A central vanadate(V) unit serves to grip four identical chiralmonomeric vanadyl(V) units together, by which a potassium ion sits on top of the four flanking unitsthrough carbonyl coordinations and serves to hold the whole cluster by cooperation with the centralvanadate(V) unit. In comparison with the corresponding monomeric vanadyl(V) methoxide complex, thecluster complex was utilized to facilitate the asymmetric aerobic oxidations of various racemic-hydroxyesters, -amides, and -thioesters with excellent selectivity factors (k_rel 40 to >500).