Chiral ligands derived from abrine. Part 7: Effect of O, S, N in aromatic ring substituents at C-1 on enantioselectivity induced by tetrahydro-β-carboline ligands in diethylzinc addition to aldehydes
The effect of O, S and N atoms in aromatic ring substituents at C-1 position of tetrahydro-β-carboline ligands on the enantioselectivity of diethylzincadditions to benzaldehyde was studied when esters or tertiary alcohol functions were present at C-3. A mechanism is proposed to explain why the ester ligands 2c and 2d, in which the pyridyl N atom is at C′-2 in 2c and at C′-3 in 2d, catalyzed the addition
当在C-3处存在酯或叔醇官能团时,研究了四氢-β-咔啉配体的C-1位芳香环取代基中的O,S和N原子对二乙基锌加成苯甲醛的对映选择性的影响。提出了一种机制来解释为什么吡啶基N原子位于2c的C'-2和位于2d的C'-3的酯配体2c和2d催化二乙基锌与苯甲醛的加成反应而形成(R) -和(S1-苯基-1-丙醇的β-对映体。还提出了一种解释,即在添加二乙基锌期间,叔醇3c诱导的中等对映选择性与3d诱导的非常小的对映选择性(在C-1处具有3-吡啶基功能)有关。C-1处的-CH 2 - t -Bu取代基导致很高的对映选择性。
The first catalytic asymmetric addition of diethylzinc to aldehyde promoted by chiral thiourea
作者:Zhi Guo Qiao、Tian Hua Shen、Zhen Fang Fu、Jun Qi Li、Hong Wang、Qing Bao Song
DOI:10.1016/j.cclet.2011.07.015
日期:2011.11
Abstract A series of C2 -symmetric and asymmetricchiral thiourea derivatives were synthesized from commercial l -phenylalanine. All of the new compounds have been fully characterized by IR, 1 H NMR, 13 C NMR, MS spectra and elemental analyses. The chiral thioureas were used as chiralligands in the catalytic enantioselective ethylation of aldehydes with diethylzinc, the corresponding sec-alcohols
摘要从商品化的1-苯丙氨酸合成了一系列C 2对称和不对称的手性硫脲衍生物。所有新化合物均已通过IR,1 H NMR,13 C NMR,MS光谱和元素分析进行了全面表征。在条件优化后,手性硫脲被用作醛与二乙基锌催化醛的对映选择性乙基化的手性配体,获得了相应的仲醇,具有优异的对映选择性(最高87.1%ee)和高收率(最高76.7%)。
Enantioselective Alkylation of Aldehydes with Diethylzinc Catalyzed by C<sub>2</sub>-Symmetric Ligands
作者:David Williams、Mark Fromhold
DOI:10.1055/s-1997-6125
日期:1997.6
The C2-symmetric pyridine 1, incorporating two units of (-)-ephedrine, is an effective catalyst for the enantioselective reactions of diethylzinc with a series of aromatic aldehydes. The propanol products possess the S-configuration. This result is a significant reversal of stereochemistry based upon literature precendents and our direct comparisons with reactions catalyzed by the corresponding C2-symmetric xylene 2.
Chiral ligands derived from abrine. Part 6: Importance of a bulky N-alkyl group in indole-containing chiral β-tertiary amino alcohols for controlling enantioselectivity in addition of diethylzinc toward aldehydes
作者:Wei-Min Dai、Hua-Jie Zhu、Xiao-Jiang Hao
DOI:10.1016/s0957-4166(00)00189-0
日期:2000.6
A number of chiral beta-amino alcohols possessing a 3-indolylmethyl group have been synthesized from the alkaloid (S)-abrine and elucidated for potency in the catalytic enantioselective ethylation of PhCHO with Et2Zn. In general, the secondary amines 15a-d bearing a dialkylhydroxymethyl group induced (R)-1-phenyl-1-propanol, whereas 15e-g and 18 bearing a diarylhydroxymethyl group favored the (S)-enantiomer. In contrast, the beta-tertiary amino alcohols 20b d and 21 produced (R)-1-phenyl-1-propanol. regardless of the substituents at the carbon bearing the hydroxy group. Enantiomeric excess of 87.5% was obtained for (R)-1-phenyl-1-propanol using ligand 21 as the promoter. Eleven substituted benzaldehydes and naphth-aldehydes were examined for enantioselective ethylation by using 21 and the chiral alcohols were obtained in 93-97% ee, except for o-BrC6H4CHO and p-Me2NC6H4CHO. Excellent enantioselectivity was also observed in the ethylation of cyclohexanecarboxaldehyde (94.8% ee) and 2-thiophenecarboxaldehyde (94.9% ee) by using catalytic 21. The anti 5/4/4-fused tricyclic TS I was proposed to rationalize the asymmetric induction. The diethylhydroxymethyl and N-2-t-butylethyl groups are believed to enforce the preference for the anti-TS(R) I and it results in high enantioselectivity. (C) 2000 Elsevier Science Ltd. All rights reserved.
Thermophysical Properties of Imidazolium-Functionalized Binols and Their Application in Asymmetric Catalysis
作者:Marc Vidal、Andreea R. Schmitzer
DOI:10.1021/om500123x
日期:2014.7.14
We report here the thermophysical properties of a new family of imidazolium-functionalized binaphthols. These properties are influenced by the position of the imidazolium moieties on the binaphthol skeleton, the counteranions, and the length of the carbon chain on the imidazolium moieties. The ionic character of these molecules was also exploited to develop ligands for the catalytic aldehyde ethylation reaction in ionic liquid media. We were able to easily recover both the ionic ligands and the ionic liquid solvent, and the reaction afforded good to excellent yields, with average selectivity.