Asymmetric synthesis XXVII: Asymmetric catalytic trimethylsilylcyanation of aldehydes by novel Ti-chiral Schiff base complexes

Enantioselective catalytic trimethylsilylcyanations of aldehydes with 48% to 92% e.e. have been studied using the novel Ti-chiral Schiff base complexes. We have found that the catalyst led to high enantoselectivity when the molar ratio of the Schiff base 1 to Ti(O-i-Pr)₄ was 2:1.     

微波相转移催化合成DL—苯丙氨酸

在微波作用下,仅用1min便完成了苯甲醛亚胺的固—液相转移催化苄基化反应,然后经酸水解得到d1—苯丙氨酸,全程总产率为62.5×10(-2)。     

在PVA存在下Os-SnCl_2-亮绿离子缔合体系的研究高纯镍中微量Os的测定

本文研究了Os-SnCl_2-PVA-亮绿离子缔合体系的显色反应,摩尔吸光系数ε_(434)为5.6×10~6L·mol~(-1)·cm~(-1),锇含量在0.1～0.7μg/25mL范围内遵守比耳定律,室温下显色后,吸光度在110min内稳定。研究了30种外来离子的影响,并进行了高纯镍中微量锇的测定。     

用手性高效液相色谱对β—羟基酯化合物进行对映体分离

本文利用手性ＯＤ柱在高效液相色谱上对光活性β－羟基酯类化合物进行了对映体分离，达到了较好的分离效果，并通过讨论手性ＯＤ涂附物的结构与该类化合物的作用方式，解释了不同的该类化合物的色谱分离效果。     

(1R,2S)或(1S,2R)-1,2-二苯基-2-氨基乙醇衍生物手性配体的合成及其用于不对称催化反应

重点报道了以（１Ｒ，２Ｓ）或（１Ｓ，２Ｒ）－１，２－二苯基－２－氨基乙醇衍生物手性配体的合成及其用于不对称催化反应的研究，如去氢氨基酸的氢化、醛的乙基锌加成、酮的还原、活泼亚甲基化合物的烷基化、醛的硅腈化和瑞福马斯基反应等．研究了手性配体的结构、底物和反应条件等对上述反应的对映选择性和催化活性的影响．     

A highly enantioselective hetero-Diels-Alder reaction of aldehydes with Danishefsky's diene catalyzed by chiral titanium(IV) 5,5',6,6',7,7',8,8'-octahydro-1,1'-bi-2-naphthol complexes

The catalytic effect of chiral Lewis acids on the hetero-Diels-Alder reaction between aldehydes and Danishefsky's diene (1) has been investigated. A variety of combinations of different ligands and Lewis acids have been examined as catalysts for the hetero-Diels-Alder reaction between benzaldehyde and 1, and it has been found that the readily accessible Ti(IV)-H(8)-BINOL (TiHBOL) complex is a very effective catalyst for the reaction, leading to products with very high enantioselectivity (up to 99% ee) and yield (92%). The hetero-Diels-Alder reaction of other aldehydes with 1 under the catalysis of TiHBOL is a general reaction which proceeds well with very high enantioselectivity and isolated yield for various aldehydes at 0 degrees C to room temperature. Based on the experimental results, the proposed mechanism of the hetero-Diels-Alder reaction and the dihedral angle effects of ligands are discussed.     

A mild and efficient cyanosilylation of ketones catalyzed by a Lewis acid-Lewis base bifunctional catalyst

A new family of bifunctional catalysts (N-oxides-Ti(OⁱPr)₄ (2:1)) containing a Lewis acid and a Lewis base was developed and applied to the catalytic cyanosilylation of ketones. Utilizing rac((1R,2S) and (1S,2R))-1-(2′-pyridylmethyl)-2-diphenylhydroxymethylpyrrolidine N-oxide-titanium (2:1) complex and N-benzyl-diethanolamine N-oxide-titanium (2:1) complex as catalysts, the cyanosilylation products were obtained in 42-97% yield. Based on experimental phenomena and kinetic studies, a catalytic cycle was proposed to explain the remarkable activities of these catalysts. Investigations indicated that rac((1R,2S) and (1S,2R))-1-(2′-pyridylmethyl)-2-diphenylhydroxymethylpyrrolidine N-oxide-titanium (2:1) complex and N-benzyl-diethanolamine N-oxide-titanium (2:1) complex should promote the reaction via a dual activation of the ketone by the titanium and TMSCN by the N-oxide.     

Asymmetric Synthesis VIII: Enantioselective Synthesis of (R) or (S)-α-Substituted Benzylamines VIA Chiral Pinanone Ketimine Template

An excellent asymmetric synthesis of both (R) and (S)-α-substituted benzylamines in optical purity 90.4–99.9% has been achieved by alkylation of a chiral ketimine, prepared from pinanone and benzylamine. Diastereoselectivity in the alkylation is not dependent on the alkyl halides.     

Asymmetric Synthesis. VII. Double Stereodifferentiation in Allylation of Ketimines Bearing Two Chiral Auxiliaries. Application to Enantioselective Synthesis of α-Allylglycine

A double asymmetric induction has been observed in allylation of the imines derived from (+)-camphor, (+)- and (-)- 2-hydroxypinan-3-ones with (+)- and (-)-menthyl glycinates. After hydrolysis of the allylated intermediates, (R)- and (S)-α-allylglycines are obtained in 3–90% optical yields.     

Solid-Liquid Phase Transfer Catalytic Synthesis XII

The anion derived from diethyl malonate reacts with a series of halides readly under microwave irradiation, and the isolated yield of alkylated products varying from 64% to 86%.