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1.
The asymmetric syntheses of novel dihydroxyhomoprolines have been achieved using the doubly diastereoselective conjugate additions of the antipodes of lithium N-benzyl-N-(α-methylbenzyl)amide to a set of four chiral α,β-unsaturated esters (derived from d-pentoses) as one of the key steps. A full account of the diastereoselectivity observed in these conjugate additions is presented and the stereochemical outcomes of these reactions have been established unambiguously via a combination of hydrogenolytic chemical correlation and single crystal X-ray diffraction analyses. A tandem hydrogenolysis/intramolecular reductive amination reaction was then used to create the corresponding enantiopure pyrrolidines, providing access to (2′S,3′S,4′R)-dihydroxyhomoproline and (2′S,3′R,4′S)-dihydroxyhomoproline after deprotection. 相似文献
2.
《Tetrahedron letters》2014,55(50):6891-6894
A highly efficient pyrrolidine-derived atropisomeric amino alcohol, (Sa)-1-[2-diphenylhydroxymethyl-6-(trifluoromethyl)phenyl]-2-(1-pyrrolido)methyl-1H-pyrrole, has been synthesized as a chiral ligand for the enantioselective addition of diethylzinc to some prochiral aldehydes to afford (S)-alcohols. The conversion rates were close to quantitative with good to excellent enantiomeric excesses (up to 95% ee). 相似文献
3.
Tomoyuki Esumi 《Tetrahedron letters》2008,49(48):6846-6849
The conjugate addition of lithium divinylcuprate to (4S,2′E)-3-(6′-TBDPS-3′-methylhex-2′-enoyl)-4-phenyloxazolidin-2-one proceeded efficiently to create a chiral all-carbon quaternary center with a high diastereoselectivity (R:S = 95:5). The absolute configuration of the newly generated chiral center was confirmed by applying this methodology to the total synthesis of (+)-bakuchiol. 相似文献
4.
Kyohei Kawashima Takehiro Sato Masamichi Ogasawara Ken Kamikawa Seiji Mori 《Journal of computational chemistry》2019,40(1):113-118
Recently, planar-chiral phosphine-olefin ligands based on (η6-arene)chromium(0) and (η5-cyclopentadienyl)manganese(I), which are known as first- and second-generation, respectively, have been developed. These ligands were employed for Rh-catalyzed asymmetric 1,4-addition to enones. First-generation ligands involve high enantioselectivity for cyclic enones (>98% ee). Second-generation ligands involve high enantioselectivity for not only cyclic enones but also for acyclic enones (>98% ee). In this study, we have performed DFT calculations to investigate the origin of enantioselectivity. The theoretical values of enantioselectivities were found to be in good agreement with the experimental values obtained for a cyclic enone, 2-cyclopenten-1-one, using both the first- and second-generation ligands. Regarding an acyclic enone, 3-penten-2-one, it was found that the s-cis type decreases the enantioselectivity because the transition states in the s-cis type have a large steric repulsion. Energy decomposition analysis (EDA) and natural bond orbital (NBO) analysis indicate that it is important to study the orbital interactions in the transition states of the insertion step for the acyclic enone attacked from si-face with the second-generation ligand. © 2018 Wiley Periodicals, Inc. 相似文献
5.
1,4-Addition of arylboronic acid to trans-β-arylenals proceeded smoothly in acetone-water (10/1) at 10-25 °C in the presence of [Pd(S,S-chiraphos)(PhCN)2](SbF6)2 (0.5 mol %), AgX (X = BF4, SbF6, 10 mol %) and aqueous 42% HBF4 to afford optically active 3,3-diarylalkanals with high enantioselectivities in a range of 86-97% ee. The protocol provided a method for short-step synthesis of optically active (+)-(R)-CDP 840. 相似文献
6.
《Tetrahedron》2014,70(21):3491-3501
The asymmetric syntheses of methyl N-Boc-2-deoxy-2-amino-l-erythroside and methyl N-Boc-2-deoxy-2-amino-d-threoside have been achieved from sorbic acid, in six and eight steps, and in 35 and 13% overall yield, respectively. Diastereoselective aminohydroxylation of tert-butyl sorbate gives access to two diastereoisomeric α-hydroxy-β-amino-γ,δ-unsaturated esters. Reduction of the ester functionality and ozonolysis of the double bond gives the corresponding aldehyde, which exists exclusively in the ring-closed (furanose) form. An alternative synthesis of methyl N-Boc-2-deoxy-2-amino-l-erythroside was also developed, reliant on aminohydroxylation of an α,β-unsaturated ester bearing an acetal functionality at the γ-position, and this synthesis proceeded in five steps and 54% overall yield from acrolein diethyl acetal. This approach was extended to permit the synthesis of methyl N-Boc-2,3-dideoxy-3-amino-l-arabinopyranoside in six steps and 58% overall yield from ethyl 3,3-diethoxypropanote. 相似文献
7.
Masafumi Tamura Hayato Ogata Yuu Ishida Yasunori Takahashi 《Tetrahedron letters》2017,58(40):3808-3813
Pd-catalyzed asymmetric 1,4-addition of phenylboronic acid to α,β-unsaturated carbonyl compounds was developed using chiral 1,10-phenanthroline derivative as ligand. Good yields (up to 97%), and high enantioselectivities (up to 97% ee) were achieved. 相似文献
8.
Stephen G. Davies Ai M. FletcherJames A. Lee Thomas J.A. LorkinPaul M. Roberts James E. Thomson 《Tetrahedron》2013
Asymmetric syntheses of (−)-martinellic acid and (−)-4-epi-martinellic acid were achieved in 20 steps from commercially available starting materials using a diastereodivergent strategy. The conjugate addition of lithium (R)-N-allyl-N-(α-methyl-p-methoxybenzyl)amide to tert-butyl (E)-3-[2′-(N,N-diallylamino)-5′-bromophenyl]propenoate and alkylation of the resultant β-amino ester with methyl bromoacetate were used as the key steps to install the C(9b) and C(3a) stereogenic centres, respectively. Subsequent cyclisation to the corresponding pyrroloquinolin-2-one and reduction of the C(4)-carbonyl group was followed by two complementary procedures for olefination and concomitant intramolecular Michael addition, which gave both C(4)-epimers of this tricyclic molecular architecture in >99:1 dr. Subsequent elaboration of these templates provided access to (−)-martinellic acid and, for the first time, (−)-4-epi-martinellic acid. 相似文献
9.
10.
Emmanuel Riguet 《Tetrahedron letters》2009,50(29):4283-1707
Novel guanidinyl pyrrolidine salts are useful bifunctional organocatalysts for the asymmetric addition of malonates to enones. These organocatalysts are effective under a wide range of reaction conditions and afford products in high yield and enantioselectivity. 相似文献
11.
Kazuhiro Matsumoto 《Tetrahedron letters》2004,45(11):2385-2388
Pentagonal bipyramidal Hf(salen) complex 1 was found to serve as a catalyst for 1,4-addition reaction of thiol to N-(2-alkenoyl)-2-oxazolidinones. 相似文献
12.
《Tetrahedron letters》2019,60(29):1913-1917
A series of bifunctional spiro ligands bearing “carboxamide–phosphine oxide” groups and ethylzinc carboxamidates from these ligands as catalysts for Et2Zn additions to aldehydes were reported. Excellent yields were obtained with moderate ee′s in Et2Zn additions to benzaldehyde derivatives, implying effectiveness of our newly designed catalytic structures as well as mediocre stereocontrol by these chiral ligands. Possible transition states were suggested based on the crystal structures of two ligands. 相似文献
13.
噻唑烷类配体的手性结构及其在催化苯乙酮不对称硅氢化反应中的应用研究 总被引:1,自引:0,他引:1
用分级结晶或柱层析方法对2-(2-吡啶基)-4-羧甲基-1,3-噻唑烷(A)及2-甲基-2-(2-吡啶基)-4-羧甲基-1,3-噻唑烷(B)两种手性配体进行提纯,分别考察了其与[Rh(COD)Cl]2制备的在位催化剂催化苯乙酮的不对称硅氢化反应,发现只有噻唑烷环上的C4位手性中心对催化反应结果有影响,其C2位手性中心在Rh(1)催化下发生了快速差向异构化反应. 相似文献
14.
Yan Xing 《Tetrahedron letters》2006,47(26):4501-4503
Chiral PNNP ligand II and [IrHCl2(COD)]2 were applied for the first time in the asymmetric transfer hydrogenation of aromatic ketones with HCOONa in water, giving the corresponding optical alcohols in high yield and excellent enantioselectivity (up to 99% ee). Particularly, the reduction of propiophenone proceeded smoothly at a substrate to catalyst molar ratio of 8000, without compromising the ee values obtained. 相似文献
15.
The 4-nitrophenyl ether is an efficient directing group in the asymmetric aminohydroxylation reaction of homoallylic ether derivatives. Either regioisomeric product can be obtained with useful levels of enantioselectivity allowing for the short enantioselective synthesis of GABOB and homoserine derivatives. A model based on substrate-catalyst interactions is presented to explain the regio- and enantioselectivity of the aminohydroxylation reactions. 相似文献
16.
17.
Novel chiral multidentate P3N4-type ligand for asymmetric transfer hydrogenation of aromatic ketones
Novel chiral multidentate P3N4-type ligand has been synthesized and characterized by NMR and HRMS. Using i-PrOH as solvent and hydrogen source, asymmetric transfer hydrogenation of various ketones was investigated. The catalyst generated in situ from chiral multidentate aminophosphine ligand (R,R,R,R)-3 and IrCl(CO)(PPh3)2 exhibited highly catalytic activity and excellent enantioselectivity under mild conditions, achieving the corresponding chiral alcohols with up to 99% yield and 99% ee. 相似文献
18.
Itaru Sato Yasushi Ohgo Daisuke Nishiyama Kenso Soai 《Journal of organometallic chemistry》2007,692(9):1783-1787
Asymmetric autocatalysis of 2-alkynyl-5-pyrimidyl alkanol is employed as a chiral sensor of 20 amino acids. Asymmetric autocatalysis using amino acids as chiral initiators gave pyrimidyl alkanols of the absolute configurations that were correlated with those of the amino acids. The enantiomeric excesses of pyrimidyl alkanol are invariably high even when the enantiomeric excess of amino acids is as low as 0.1%. Thus, by determining the absolute configuration of pyrimidyl alkanol with high enantiomeric excess, one can determine the absolute configuration of amino acids even when their enantiomeric excess is low. 相似文献
19.
A mechanistic study was carried out for the asymmetric Michael addition reaction of malonates to enones catalyzed by a primary amino acid lithium salt to elucidate the origin of the asymmetric induction. A primary β-amino acid salt catalyst, O-TBDPS β-homoserine lithium salt, exhibited much higher enantioselectivity than that achieved with the corresponding catalysts derived from α- and γ-amino acids for this reaction. Detailed studies of the transition states with DFT calculations revealed that the lithium cation and carboxylate group of the β-amino acid salt catalyst have important roles in achieving high enantioselectivity in the Michael addition reaction of malonates to enones. 相似文献
20.
Hiroshi Akutsu Kosuke Nakashima Shin-ichi Hirashima Hikari Matsumoto Yuji Koseki Tsuyoshi Miura 《Tetrahedron》2019,75(16):2431-2435
The asymmetric direct bisvinylogous conjugate addition of 5-benzylfurfural derivatives to nitroalkenes using a thiourea organocatalyst resulted in a corresponding ε-regioselective addition products in high yields and up to 95% enantiomeric excess. 相似文献