共查询到20条相似文献,搜索用时 0 毫秒
1.
《Tetrahedron: Asymmetry》2005,16(4):761-771
A number of bicyclic chiral sultams were synthesized based on 1,3-dipolar cycloaddition reactions of nitrile oxides and nitrones with prop-1-ene-1,3-sultone. The corresponding N-enoyl sultams were prepared by acylation. Their relative effectiveness as new chiral auxiliaries in asymmetric synthesis was evaluated for the asymmetric Diels–Alder reactions with cyclopentadiene. Good chemical yield and excellent endo selectivity were observed. The relationship between the structure and their effectiveness in promoting asymmetric induction of the synthetic chiral sultams was investigated. 相似文献
2.
《Tetrahedron》1987,43(9):1969-2004
3.
The chiral enoates, , readily available in two simple steps from (+)-camphor, Undergo asymmetric conjugate addition with the Gilman reagent LiBu2Cu. Chemical yields are high (70–90%) and in the case of the naphthyl-substituted enoate excellent diastereoselectivity (95% ) is observed. 3-Methyl-heptan-l-ol of correspondingly high enantiomeric purity is obtained by reduction of the conjugate adduct with lithium aluminium hydride. 相似文献
4.
Asymmetric aldol reactions of oxazolidinones as chiral auxiliaries have been achieved and attracted significant consideration as one of the most powerful synthetic tools for the carbon–carbon bond-forming reactions. The methodology has been highly successful in the stereoselective construction of a number of natural products, antibiotics, and other medicinally important compounds. The present review is focused on the utility and versatility of oxazolidinones (Evans chiral auxiliaries) in the asymmetric aldol condensations for the total synthesis of natural products and complex targets. 相似文献
5.
Replacement of the 2-keto group of readily available di(endo-3-camphoryl) diselenide with oxime or O-benzoyloxime substituents, followed by conversion into the corresponding selenenyl triflates, produced highly effective chiral selenium electrophiles for the asymmetric oxyselenenylation of alkenes in the presence of methanol. 相似文献
6.
《Tetrahedron: Asymmetry》2000,11(2):371-374
Two new chiral glyco-oxazolidin-2-one auxiliaries based on d-glucose are described. Some N-acyl derivatives were synthesized and used in dialkylboron-mediated asymmetric aldol reactions. All reactions delivered as the major diastereomer those predicted by the Zimmerman–Traxler model and were separated by column chromatography and mostly isolated in moderate to good yields. 相似文献
7.
[reaction: see text] Highly diastereoselective biaryl Suzuki coupling reactions of (1R)-1-(2-iodo or bromophenyl)-2-(R)-(4-tolylsulfinyl)-1-ethanol derivatives with various aryl- or naphthylboronic acids (or esters) were performed with high yields (up to 99%) and an excellent control of the axial chirality (up to 98% de). 相似文献
8.
9.
Investigations on modified guanidines, prepared by newly developed methods, as potential chiral auxiliaries led to reasonable asymmetric induction not only in catalytic but also in stoichiometric asymmetric syntheses. These guanidine-mediated reactions may contribute to the development of green chemistry because of their possible application as re-cyclable (economically favored) and easily functionalizable (widely applicable) auxiliaries. 相似文献
10.
11.
Planar chiral hydroxy derivatives of [2.2]paracyclophane as auxiliaries for asymmetric allylboration
N. V. Vorontsova R. P. Zhuravsky E. V. Sergeeva E. V. Vorontsov Z. A. Starikova V. I. Rozenberg 《Russian Chemical Bulletin》2007,56(11):2225-2231
Allylboronic esters with various structures were synthesized for the first time based on [2.2]paracyclophane derivatives containing
one or two hydroxy groups. It was demonstrated that these esters can be used as chiral inductors in the asymmetric allylboration
of benzaldehyde. The highest enantiomeric excess of 1-phenylbut-3-en-1-ol (60%) was achieved in the reactions with acyclic
bis-O,O′-(paracyclophanyl) allylboronates based on (S)-4-hydroxy-and (S)-12-bromo-4-hydroxy[2.2]paracyclophanes. (S)-4-Hydroxy[2.2]paracyclophane was studied by X-ray diffraction.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2149–2155, November, 2007. 相似文献
12.
13.
2-Bromopyridine and 2-bromo-6-methoxymethylpyridine reacted with an excess of 1-phenylethylamine at reflux giving the aminopyridine derivatives 3a and 3b respectively. 相似文献
14.
Irène Nicolas 《Tetrahedron letters》2008,49(13):2111-2113
The asymmetric addition of diazoacetophenone to styrene derivatives to give optically active cyclopropyl ketones (ee up to 86%) was carried out by using chiral ruthenium porphyrins as homogeneous catalysts. 相似文献
15.
A new chiral auxiliary was designed and easily prepared from a Diels-Alder cycloadduct of an enantiomerically pure anthracene with maleimide. Excellent diastereoselectivities in Diels-Alder reactions, conjugate additions, and aldol reactions employing these auxiliaries are now reported. 相似文献
16.
The complex derived from Taniaphos ligand 4 and CuBr*Me2S catalyzes the asymmetric addition of Grignard reagents to 3-bromopropenyl esters 1 to provide allylic esters 2 in high yields and high chemio-, regio-, and enantioselectivities. The work demonstrates that allylic asymmetric alkylation (AAA) can be done on substrates bearing a heteroatom at the gamma-position. The method is a practical route to chiral, nonracemic allylic alcohols. The use of functionalized substrates 1 or Grignard reagents leads to more complex products 2, which can be further manipulated as demonstrated in conversion to (S)-5-ethyl-2(5H)-furanone 6 and (S)-benzoic acid-cyclopent-2-enyl ester 7. 相似文献
17.
New chiral auxiliaries derived from levoglucosenone were developed in a simple and efficient way and evaluated as chiral inductors in asymmetric Diels-Alder reactions between the corresponding acrylate derivatives and cyclopentadiene. The results showed an important influence of the absolute configuration of the C(2) center of the auxiliary on the level of stereoinduction obtained. 相似文献
18.
Spino C 《Chemical communications (Cambridge, England)》2011,47(17):4872-4883
Two chiral auxiliaries and the role they play in the preparation of chiral carbonyl compounds and heterocyclic compounds are presented. Key reactions include S(N)2' displacements, Mitsunobu with hydrazoic acid, and 3,3-sigmatropic rearrangements. One of the auxiliaries serves many functions and is removed either by oxidative cleavage or RCM reaction. 相似文献
19.