N-(4-[2.2]paracyclophanyl)-2?hydroxyacetophenone imine: An effective paracyclophane Schiff-base ligand for use in catalytic asymmetric cyclopropanation reactions

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• 作者：Douglas S. Masterson^b ; Caitlyne Shirley^b ; Daniel T. Glatzhofer^a ; ^{dtglatzhofer@ou.edu}
• 关键词：Chiral [2.2]paracyclophane derivatives ; Chiral Schiff-base ; Asymmetric cyclopropanation ; Asymmetric catalysis ; Copper(II)-catalyzed cyclopropanation
• 刊名：Journal of Molecular Catalysis A: Chemical
• 出版年：2012
• 出版时间：September, 2012
• 年：2012
• 卷：361-362
• 期：Complete
• 页码：111-115
• 全文大小：350 K

文摘

The synthesis of planar chiral N-(4-[2.2]paracyclophanyl)-2?hydroxyacetophenone imine (5) and its use as a ligand for the copper(II) catalyzed cyclopropanation of styrene and stilbene derivatives using diazoesters is presented. Catalyst loadings of 0.1 mol % gave conversions of >80 % (turnover numbers approaching 1000) for styrene and its derivatives. When enantiomerically enriched (R)-5 was used to form the catalyst for cyclopropanation of styrene using ethyldiazoacetate, the cyclopropane products were obtained in a trans/cis ratio of 1.9-1 and 75.8 % and 60.5 % ee (corrected), respectively. The use of t-butyldiazoacetate resulted in an increased trans/cis ratio of 4.6-1 and 88.2 % and 77.9 % ee, respectively. Enantioselectivities of up to 95 % ee were observed. These are among the highest enantioselectivities observed for asymmetric reactions using catalysts where chirality is solely derived from the paracyclophanyl moiety. When compared to its non-methylated analog, the simple presence of a methyl group on the carbon of the imine moiety in 5 resulted in an average increase in enantioselectivity of ca. 60 % ee for a variety of substrates. The origin of this dramatic improvement in selectivity is discussed.