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Approach to a better understanding and modelling of b-pyrrolidinoalcohol ligands for enantioselective alkylation

Gonsalves, Antonio M. d'A. Rocha; Serra, M. Elisa S.; Murtinho, Dina ( Departamento de Quimica, Faculdade de Ciencias e Tecnologia, Universidade de Coimbra, Coimbra 3004-535, Port.). Journal of Molecular Catalysis A: Chemical, 250(1-2), 104-113 (English) 2006 Elsevier B.V. CODEN: JMCCF2. ISSN: 1381-1169. DOCUMENT TYPE: Journal CA Section: 25 (Benzene, Its Derivatives, and Condensed Benzenoid Compounds) A series of pyrrolidine-based b-amino alcs. (I; R = CH2Ph, 1-naphthylmethyl, (R)- or (S)-1-phenylethyl), (II), and (III) derived from malic acid, citramalic acid and pantolactone with primary amines were prepd. and their activity as chiral ligands in the enantioselective alkylation of benzaldehyde using diethylzinc was studied. The new ligands tested (33-56% ee, enantiomeric excess of product 1-phenyl-1-propanol) are less selective than the tartaric acid derivs. (IV; R1 = benzyl, hexyl, 1-naphthylmethyl) (72-80% ee). Among the malic acid derivs. I (38-56% ee), there were no significant changes in enantiomeric excess (ee) with the N-substituent, contrary to what was obsd. with the tartaric acid derivs.Several reagents such as 691-84-9 is used here. IV where visible changes were obsd. with the nature of this group. The ligands obtained using both enantiomers of 1-phenylethylamine I (R = (R)-1-phenylethyl) (56% ee) and I (R = (S)-1-phenylethyl) (38% ee) showed the effect of an addnl. chiral center directly adjacent to the nitrogen. The presence of the (R) chiral center proved to be irrelevant while the (S) chiral center caused a decrease in the ee of the reaction product. The selectivity obsd. with the citramalic acid deriv. II (33% ee) was much lower than in the case of the malic acid derivs. I (38-56% ee). With the pantolactone deriv. III (56% ee), results were identical to the malic acid derivs. I. The structural changes which were introduced in the novel ligands showed no advantage relatively to the previously studied ligands.In this study，691-84-9 is also used. However, they are useful in helping to achieve a better understanding of the induction of chirality by pyrrolidinoalc. chiral ligands and can therefore be helpful for the design of more efficient inducers of chirality. In order to better understand the differences in selectivity between these new ligands I-III and the tartaric acid derivs. IV, namely if they are due to the absence of the second hydroxy, the second chiral center or both, a ligand (V) with two chiral centers but only one free hydroxy group was prepd. and tested. When the ligand V was used in the enantioselective alkylation of benzaldehyde, (R)-1-phenyl-1-propanol was obtained with an ee of 43%. Comparing to the selectivity of the various N-benzyl ligands, it is clear that this ee for V is most similar to those obtained with the malic, citramalic and pantolactone ligands I-III. This seems to indicate that it is the lack of the second free hydroxy and not of a second chiral center which is responsible for the lower selectivity of the new ligands herein described. ..

Approach to a better understanding and modelling of b-pyrrolidinoalcohol ligands for enantioselective alkylation

Gonsalves, Antonio M. d'A. Rocha; Serra, M. Elisa S.; Murtinho, Dina ( Departamento de Quimica, Faculdade de Ciencias e Tecnologia, Universidade de Coimbra, Coimbra 3004-535, Port.). Journal of Molecular Catalysis A: Chemical, 250(1-2), 104-113 (English) 2006 Elsevier B.V. CODEN: JMCCF2. ISSN: 1381-1169. DOCUMENT TYPE: Journal CA Section: 25 (Benzene, Its Derivatives, and Condensed Benzenoid Compounds) A series of pyrrolidine-based b-amino alcs. (I; R = CH2Ph, 1-naphthylmethyl, (R)- or (S)-1-phenylethyl), (II), and (III) derived from malic acid, citramalic acid and pantolactone with primary amines were prepd. and their activity as chiral ligands in the enantioselective alkylation of benzaldehyde using diethylzinc was studied. The new ligands tested (33-56% ee, enantiomeric excess of product 1-phenyl-1-propanol) are less selective than the tartaric acid derivs. (IV; R1 = benzyl, hexyl, 1-naphthylmethyl) (72-80% ee). Among the malic acid derivs. I (38-56% ee), there were no significant changes in enantiomeric excess (ee) with the N-substituent, contrary to what was obsd. with the tartaric acid derivs.Several reagents such as 691-84-9 is used here. IV where visible changes were obsd. with the nature of this group. The ligands obtained using both enantiomers of 1-phenylethylamine I (R = (R)-1-phenylethyl) (56% ee) and I (R = (S)-1-phenylethyl) (38% ee) showed the effect of an addnl. chiral center directly adjacent to the nitrogen. The presence of the (R) chiral center proved to be irrelevant while the (S) chiral center caused a decrease in the ee of the reaction product. The selectivity obsd. with the citramalic acid deriv. II (33% ee) was much lower than in the case of the malic acid derivs. I (38-56% ee). With the pantolactone deriv. III (56% ee), results were identical to the malic acid derivs. I. The structural changes which were introduced in the novel ligands showed no advantage relatively to the previously studied ligands.In this study，691-84-9 is also used. However, they are useful in helping to achieve a better understanding of the induction of chirality by pyrrolidinoalc. chiral ligands and can therefore be helpful for the design of more efficient inducers of chirality. In order to better understand the differences in selectivity between these new ligands I-III and the tartaric acid derivs. IV, namely if they are due to the absence of the second hydroxy, the second chiral center or both, a ligand (V) with two chiral centers but only one free hydroxy group was prepd. and tested. When the ligand V was used in the enantioselective alkylation of benzaldehyde, (R)-1-phenyl-1-propanol was obtained with an ee of 43%. Comparing to the selectivity of the various N-benzyl ligands, it is clear that this ee for V is most similar to those obtained with the malic, citramalic and pantolactone ligands I-III. This seems to indicate that it is the lack of the second free hydroxy and not of a second chiral center which is responsible for the lower selectivity of the new ligands herein described. ..