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Diamine‐Catalyzed Addition of ZnEt 2 to PhC(O)CF 3 : Two Mechanisms and Autocatalytic Asymmetric Enhancement
Author(s) -
CalvilloBarahona Mercedes,
Casares Juan A.,
Cordovilla Carlos,
Genov Miroslav N.,
MartínezIlarduya Jesús M.,
Espinet Pablo
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201403648
Subject(s) - autocatalysis , catalysis , diamine , chemistry , medicinal chemistry , polymer chemistry , organic chemistry
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 [(NN)Zn(Et){OC(CF 3 )(Et)Ph}]. For NN 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 NN 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.