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1.
A new chiral bicyclic tetrahydropyridine derivative was synthesized from L -lysine derivatives utilizing electrochemical oxidation as a key step. Allyl alcohols were incorporated into the tetrahydropyridine derivative to afford N,O-acetals, and the reaction of the resulting N,O-acetals with a carbenoid, which was generated from Et2Zn and CH2l2, yielded cyclopropanated products in moderate diastereoselectivities. 相似文献
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Reaction of chiral acryloylhydrazide 5 derived from novel auxiliary 4 with aldehydes in the presence of DABCO affords practical levels (up to 98% de) of beta-hydroxy-alpha-methylene carbonyl derivatives, and high optical purity of both diastereomers of 6a-d and 7a-d can be obtained by changing the solvent. 相似文献
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Asymmetric epoxidation of N-enoylsultams (1, 3-15) incorporating a variety of chiral sultams as the chiral induction elements with UHP/TFAA has been studied. Both diastereomeric isomers of epoxides (2, 16-28) were obtained in high yield and moderate to high optical purity. 相似文献
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The proton affinities of 2(5H)-furanone, 1 (836 kJ/mol), 5,6-dihydro-2H-pyran-2-one, 2 (862 kJ/mol), cyclopentenone, 3 (857 kJ/mol), and cyclohexenone, 4 (863 kJ/mol), have been measured by Fourier transform ion cyclotron resonance techniques. A comparison is made with (reexamined) data concerning saturated cyclic and unsaturated aliphatic analogs. Three general observations are made. First, the basicity is found to increase with the size of the ring. Second, unsaturated lactones are more basic than their corresponding aliphatic unsaturated esters. Third, unsaturated and saturated lactones have almost identical gas-phase basicities, while unsaturated and saturated lactones have almost identical gas-phase basicities, while unsaturated cyclic ketones are more basic than their saturated analogs. All these experimental findings have been rationalized by means of ab initio calculations up to the G2(MP2,SVP) level. The basicity trends along the series are the result of two main factors: the different hybridization pattern of the carbonyl carbon as the size of the ring changes and, in the case of lactones, the nonbonding interaction between the proton attached to the carbonyl group and the ether-like oxygen which contributes to the enhanced stability of the protonated form. For unsaturated ketones the C=C double bond participates fully in the change in charge distribution induced by the protonation, while for unsaturated lactones the existence of an oxygen atom within the ring impedes this shift of the electron density. 相似文献
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de Meijere A Schirmer H Duetsch M 《Angewandte Chemie (International ed. in English)》2000,39(22):3964-4002
The metal carbene complexes, discovered by E. O. Fischer at the start of the 1960s and carrying his name, have since proved themselves to be irreplaceable building blocks for organic synthesis. In particular, since the discovery of the D?tz reaction, a formal cycloaddition of Fischer alpha,beta-unsaturated carbene complexes to alkynes with CO insertion, this area of chemistry has become increasingly interesting to organic chemists. In spite of the considerable diversity of reactions performed with these complexes, proper selection of substrates and careful adjustment of the reaction conditions have allowed, in most cases the perfectly selective preparation of individual compounds of this enormous range of products. The spectrum of new successes begins with the conventional Diels-Alder reaction of alkynylcarbene complexes and the formal regioselective [3+2] cycloaddition of alkenylcarbene complexes to alkynes. It extends much further, however, from cascade reactions with the formation of oligofunctional and oligocyclic products of impressive molecular complexity to complex, formal [3+6] cocyclizations in which six bonds are formed in a single operational step. Beyond doubt, the methodological arsenal of preparative organic chemistry cannot be imagined any more without the valuable transformations of the Fischer carbene complexes; it only remains to be seen whether one or other of the numerous new types of cocyclization products of these complexes can establish itself as a lead structure in the search for biologically active compounds. 相似文献
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Susumu Saito Keiko Hatanaka Taichi Kano Hisashi Yamamoto 《Angewandte Chemie (International ed. in English)》1998,37(24):3378-3381
A C 2 -symmetrical phenol was used as a chiral auxiliary in the asymmetric aldol reaction of chiral acetates with various aldehydes [Eq. (a)]. The reaction proceeds readily under mild conditions to provide aldol adducts with high enantioselectivity. LDA=lithium diisopropylamide. 相似文献
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The Wittig reagent [(diethoxyphosphinyl)methylidene]triphenylphosphorane (1b) has been successfully synthesized for the first time via its phosphonium triflate salt (4a), by treating (diethoxyphosphinyl)methyl triflate with triphenylphosphine. The procedure has been applied to the synthesis of other phosphoranes and phosphonium salts. The new Wittig reagents thus synthesized were treated with various aldehydes and an activated ketone, affording the corresponding alpha,beta-unsaturated phosphonates. Triphenylphosphorane 1b and triphenylphosphonium 4a led to both cis and trans isomers with the latter being predominant, while trans isomers were almost exclusively formed when tributyl reagents (1c and 4d) were used. 相似文献
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以十六烷基三甲基溴化铵(CTAB)的自组装体为模板,卵磷脂(PC)为手性添加剂,在nPC:nCTAB=1:21时,通过溶胶-凝胶法制备了螺旋介孔二氧化硅纳米棒。利用扫描电镜(FESEM)、透射电镜(TEM)、X-射线衍射以及氮气吸附-脱附等测试手段,对该纳米棒的形貌以及孔结构进行了表征。TEM显示该纳米棒的长度约为50~200nm,直径约为30~50nm。X-射线衍射表明孔道呈二维六方排列,虽然FESEM显示纳米棒左右手比例约为1:1,但通过圆二色谱表征证明该纳米棒在埃尺度下倾向于形成单一手性。结果表明,卵磷脂的手性可以传递到螺旋介孔二氧化硅纳米棒中。 相似文献
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以十六烷基三甲基溴化铵(CTAB)的自组装体为模板,卵磷脂(PC)为手性添加剂,在n PC∶nCTAB=1∶21时,通过溶胶-凝胶法制备了螺旋介孔二氧化硅纳米棒。利用扫描电镜(FESEM)、透射电镜(TEM)、X-射线衍射以及氮气吸附-脱附等测试手段,对该纳米棒的形貌以及孔结构进行了表征。TEM显示该纳米棒的长度约为50~200 nm,直径约为30~50 nm。X-射线衍射表明孔道呈二维六方排列,虽然FESEM显示纳米棒左右手比例约为1∶1,但通过圆二色谱表征证明该纳米棒在埃尺度下倾向于形成单一手性。结果表明,卵磷脂的手性可以传递到螺旋介孔二氧化硅纳米棒中。 相似文献
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This article describes a simple method for the synthesis of roxifiban, a potent glycoprotein GP IIb‐IIIa receptor antagonist, by a diastereoselective coupling approach to give >99.9% optical purity. We have also described an attempt to resolve the key synthetic intermediate by diastereomeric ester formation. Although we have been able to separate two diastereomeric esters, the removal of the chiral auxiliary led to partial racemization. 相似文献
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A new and efficient method has been developed for the diastereoselective synthesis of unnatural dipeptide analogues containing the metabolically stable phosphinic moiety, NH 2XaaPsi[P(O)OHCH 2]XaaOH, which mimics the transition state of tetrahedral geometry of a scissile peptide bond in hydrolysis by protease. The method is based upon stereospecific Michael addition of stereodefined alpha-aminoalkyl- H-phosphinates to acrylates and subsequent diastereoselective alkylation at the beta'-position of the resulting Michael adducts. 相似文献
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Asymmetric cyclopropanation of diphenylethene with diazoacetates was catalyzed by new copper-(Schiff base) complexes. The
effects of the substituents in substituted salicylaldehyde on the ee's were studied, and a 94.5% ee was achieved.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献