Diamine‐Catalyzed Addition of ZnEt2 to PhC(O)CF3: Two Mechanisms and Autocatalytic Asymmetric Enhancement |
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| Authors: | Mercedes Calvillo‐Barahona Prof. Dr. Juan A. Casares Dr. Carlos Cordovilla Dr. Miroslav N. Genov Dr. Jesús M. Martínez‐Ilarduya Prof. Dr. Pablo Espinet |
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| Affiliation: | 1. IU CINQUIMA/Química Inorgánica, Facultad de Ciencias, Universidad de Valladolid, Paseo Belén 5, 47011 Valladolid (Spain), Fax: (+34) 983423013;2. Sealife Pharma GmbH, Technopark I/Geb.B/EG, 3430 Tulln (Austria) |
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| Abstract: | NMR spectroscopic studies of the catalytic addition reaction of ZnEt2 to PhC(O)CF3 in the presence of three very efficient catalysts [TMEDA, tBuBOX, and L ; where L is a chiral diamine synthesized from optically pure (R,R)‐1,2‐diphenylethylenediamine and (S)‐2,2′‐bis‐(bromomethyl)‐1,1′‐binaphthalene] reveal large differences in their behavior. For the ligands TMEDA and tBuBOX, the catalysis shows no unusual features and proceeds via [(N?N)Zn(Et){OC(CF3)(Et)Ph}]. For N?N? L , the observation of autocatalytic asymmetric enhancement during the catalysis, and unusual inverse concentration dependence on the reaction rate, indicate the participation of an additional novel catalytic cycle that goes through a dinuclear intermediate containing one ZnEt2 and one ZnEt fragment connected by N?N and OR bridges. Interestingly, the 19F NMR signals of the main product of the reaction ([Zn(Et){OC*(CF3)(Et)Ph}]2) allowed us to assess the enantioselectivity of the processes in situ without the assistance of chiral chromatography. |
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| Keywords: | alkylation asymmetric catalysis autocatalysis ligand effects zinc |
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