共查询到20条相似文献,搜索用时 0 毫秒
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介绍了双中心协同催化作用的概念以及A型和B型两类催化剂。综述了A型催化 剂在不对称硝基-类羟醛反应、迈克尔加成反应、亚胺和醛的氢膦酰化反应、曼尼 希反应、不对称醛酮羟醛反应以及环氧开环反应中的应用;同时简要介绍了B型催 化剂在不对称合成中的应用。 相似文献
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Maria Kitamura Prof. Yoshimi Hirokawa Prof. Dr. Naoyoshi Maezaki Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(38):9911-9917
We have accomplished highly enantioselective [2,3]‐Wittig rearrangements of functionalized allyl benzyl ethers in the presence of a chiral di‐tBu‐bis(oxazoline) ligand. In various oxygenated benzylic ethers, the reactions proceeded with excellent diastereo‐ and enantioselectivities, although the presence of a methoxy substituent at the ortho‐position on the benzyl group drastically decreased the enantioselectivity. Conversely, o‐ethyl and o‐phenyl substituents had no significant effect on the selectivity. We found that the C2‐substituent of the allylic moiety played an important role in producing high enantioselectivity. Highly enantioselective [2,3]‐Wittig rearrangement in the presence of catalytic amounts of the chiral ligands is also described. 相似文献
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Bringmann G Price Mortimer AJ Keller PA Gresser MJ Garner J Breuning M 《Angewandte Chemie (International ed. in English)》2005,44(34):5384-5427
A rotationally hindered and thus stereogenic biaryl axis is the structurally and stereochemically decisive element of a steadily growing number of natural products, chiral auxiliaries, and catalysts. Thus, it is not surprising that significant advances have been made in the asymmetric synthesis of axially chiral biaryl compounds over the past decade. In addition to the classic approach (direct stereoselective aryl-aryl coupling), innovative concepts have been developed in which the asymmetric information is introduced into a preformed, but achiral-that is, symmetric or configurationally labile-biaryl compound, or in which an aryl--C single bond is stereoselectively transformed into an axis. This Review classifies these strategies according to their underlying concepts and critically evaluates their scope and limitations with reference to selected model reactions and applications. Furthermore, the preconditions required for the existence of axial chirality in biaryl compounds are discussed. 相似文献
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Itaru SatoKousuke Kadowaki Hiroki UrabeJong Hwa Jung Yoshiyuki OnoSeiji Shinkai Kenso Soai 《Tetrahedron letters》2003,44(4):721-724
Highly enantiomerically enriched (up to 96-97% ee) 5-pyrimidyl alkanol was obtained by the addition of diisopropylzinc to pyrimidine-5-carbaldehyde in the presence of the artificially designed chiral inorganic material, right- and left-handed helical silica. 相似文献
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N. V. Vorontsova V. I. Rozenberg E. V. Vorontsov O. L. Tok Yu. N. Bubnov 《Russian Chemical Bulletin》2000,49(5):912-919
Stereoselectivity of allylboration of 4-formyl[2.2]paracyclophane, 4-acetyl[2.2]paracyclophane, and 4-hydroxy-5-formyl[2.2]paracyclophane
was studied and the relative configurations of the homoallylic alcohols obtained were established. Optically pure (Sp,Sc)-(+)-4-(4-hydroxy-1-methylbut-3-enyl)[2.2]paracyclophane and (Rc,Sc)-(+)-4-hydroxy-5-(4-hydroxybut-3-enyl)[2.2]paracyclophane were synthesized. The possibility of using (Sp,Sc)-(+)-4-(4-hydroxy-4-methylbut-3-enyl)[2.2]paracyclophane as a recoverable chiral auxiliary in asymmetric allylboration of
aldehydes was demonstrated.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 914–921, May, 2000. 相似文献