Diamine-catalyzed addition of ZnEt2 to PhC(O)CF3 : two mechanisms and autocatalytic asymmetric enhancement.
Chemistry
; 20(45): 14800-6, 2014 Nov 03.
Article
em En
| MEDLINE
| ID: mdl-25223511
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 (19) F 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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01-internacional
Base de dados:
MEDLINE
Assunto principal:
Compostos Organometálicos
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Acetofenonas
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Diaminas
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Clorofluorcarbonetos de Metano
Idioma:
En
Ano de publicação:
2014
Tipo de documento:
Article