Diamine‐Catalyzed Addition of ZnEt 2 to PhC(O)CF 3 : Two Mechanisms and Autocatalytic Asymmetric Enhancement

• Published in: Chemistry : a European journal 2014-11, Vol.20 (45), p.14800-14806
• Main Authors: Calvillo‐Barahona, Mercedes, Casares, Juan A., Cordovilla, Carlos, Genov, Miroslav N., Martínez‐Ilarduya, Jesús M., Espinet, Pablo
• Format: Article
• Language: English
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201403648

NMR spectroscopic studies of the catalytic addition reaction of ZnEt 2 to PhC(O)CF 3 in the presence of three very efficient catalysts [TMEDA, t BuBOX, 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 t BuBOX, the catalysis shows no unusual features and proceeds via [(NN)Zn(Et){OC(CF 3 )(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 ZnEt 2 and one ZnEt fragment connected by NN and OR bridges. Interestingly, the 19 F NMR signals of the main product of the reaction ([Zn(Et){OC*(CF 3 )(Et)Ph}] 2 ) allowed us to assess the enantioselectivity of the processes in situ without the assistance of chiral chromatography.