共查询到20条相似文献,搜索用时 15 毫秒
1.
Gowravaram Sabitha Sambit Nayak M. Bhikshapathi J.S. Yadav 《Tetrahedron letters》2009,50(38):5428-5429
The first total synthesis of (3S,4R)-dihydroxy-(6S)-undecyl-α-pyranone 1 and total synthesis of (2S,3R,5S)-(−)-2,3-dihydroxytetradecan-5-olide 2 have been achieved in five steps in a highly stereoselective manner using Maruoka allylation, olefin cross-metathesis, and Sharpless asymmetric dihydroxylation as key steps. 相似文献
2.
Nativitat Valls 《Tetrahedron letters》2006,47(22):3701-3705
The first syntheses of (2S,3R)- and (2S,3S)-3-chloroleucine (3-chloro-d-leucines 1 and 2) have been achieved from d-3-hydroxyleucine and allo-d-3-hydroxyleucine, respectively, through the formation of the corresponding N-Cbz β-lactones, followed by a ring opening promoted by lithium chloride and a debenzylation process. 相似文献
3.
Radical-mediated opening of a chiral trisubstituted epoxy alcohol using cp2TiCl furnished the ‘2-methyl-1,3-diol’ moiety with the desired stereochemistry, which led to a total synthesis of (3R,4S,5S,9S)-3,5,9-trihydroxy-4-methylundecanoic acid δ-lactone 1. 相似文献
4.
Satyendra Kumar Pandey 《Tetrahedron letters》2006,47(25):4167-4169
An efficient and short synthesis of (2R,3R)- and (2S,3S)-β-hydroxyornithine 1a-b is described using Sharpless asymmetric dihydroxylation and regioselective nucleophilic opening of a cyclic sulfite as the key steps. 相似文献
5.
A three-step synthesis of (R)-7-hydroxycarvone (1), which is anticipated to be a valuable building block for the versatile preparation of natural products, is described. Optimization of the reaction conditions for photooxygenation and migration of (S)-α-pinene 2, tetrapropylammonium perruthenate (TPAP) oxidation of the generated alcohol, and a subsequent ring-opening reaction in the presence of Cu(OTf)2 led to the synthesis of 1 with good reproducibility. The desired product 1 was thus obtained in 46% yield over three steps. 相似文献
6.
Natalia A. LarionovaAlexandr S. Kucherenko Dmitry E. SiyutkinSergei G. Zlotin 《Tetrahedron》2011,67(10):1948-1954
Chiral ionic liquids containing (S)- or (R)-threonine amide and α,α-(S)-diphenylvalinol units were synthesized In the presence of the (S)-threonine-derived catalyst reactions between ketones with secondary carbon atom(s) at the α-position with respect to the carbonyl group and aromatic (heteroaromatic) aldehydes afforded the corresponding syn-aldols in high yields (up to 99%) and with high diastereo-(syn/anti up to 97:3) and enantioselectivity (up to 99% ee), which was maintained over three reaction cycles. 相似文献
7.
The first asymmetric total synthesis of (R)-tuberolactone, (S)-jasmine lactone and (R)-δ-decalactone
A general synthetic approach has been developed for the first asymmetric total synthesis of tuberolactone 1, jasmine lactone 2 and δ-decalactone 3. The key step is the selective hydrogenation of triple and endocyclic double bonds in the key intermediate 4. 相似文献
8.
A new route for (2S,3S,4S)-form, the physiologically active stereoisomer of dehydroxymethylepoxyquinomicin (DHMEQ), a potent NF-κB inhibitor, was established by chemoenzymatic approach. Elaboration on the asymmetric epoxidation of a p-benzoquinone monoketal with benzylcinchonidinium tert-butylhydroperoxide yielded an epoxyenone, in 79.8% ee and 57% yield in reproducible manner. By way of the transformation of this key intermediate to enantiomerically pure (2S,3S,4S)-DHMEQ, the contaminating undesired enantiomer could be effectively removed by applying Burkholderia cepacia lipase-catalyzed hydrolysis of diacylated precursor. The above integrated combination of chemical asymmetric synthesis and enzyme-catalyzed kinetic resolution enabled us to prepare active DHMEQ in a large-scale. 相似文献
9.
Gabriela Huelgas Sylvain Bernès Leticia Quintero Cecilia Anaya de Parrodi Patrick J. Walsh 《Tetrahedron》2007,63(51):12655-12664
The synthesis of atropisomeric 2-substituted benzamides 2a-e, 3a-e, and 4a-e, and characterization by X-ray structure analysis of 2d, 2e, 3c, 3e, 4c, and 4e are reported. Dynamic 1H NMR spectroscopic studies of benzamides 2b-d, 3b-d, and 4b-d indicate that only two of the four possible rotamers are present in solution, with population ratios ranging between 1.5:1 and 4.1:1. The measured free energy of activation to interconversion of the rotamers ranged from 12.4 to 18.9 kcal mol−1. Benzamides ArCON[(S)-phenethyl]2 (2e, 3e, and 4e), exhibited atropisomer ratios between 1.7:1 and 1:1, and free energies of interconversion of the rotamers ranged from 11.5 to 17.6 kcal mol−1. The highest rotation barriers were observed for the ortho-nitro derivatives 2a-e. Molecular calculations at the semiempirical level (PM3MM) gave free energies of activation for benzamides 2e and 3e of 23.6 and 12.4 kcal mol−1, respectively, which are comparable to the experimental values. 相似文献
10.
The aldol condensation reactions of α,α-diacetyl ketene-(S,S)-acetals, 1a and 1b, with aromatic aldehydes 2 in the presence of NaOH in water have been investigated. At room temperature, the base-mediated condensations proceed smoothly to afford the corresponding mono-condensed products, α-alkenoyl ketene-(S,S)-acetals 3, in high yields. At reflux temperature, the reactions produce high yields of symmetric double condensed α,α-dialkenoyl ketene-(S,S)-acetals 4 when 2 equiv of aldehyde are employed. Moreover, compounds 3 can condense with a different aldehyde to give unsymmetric double condensed α,α-dialkenoyl ketene-(S,S)-acetals 5. 相似文献
11.
Jun Lu 《Tetrahedron letters》2008,49(41):6007-6008
(1R,3S,4S)-2-Azanorbornyl-3-methanol was synthesized form (R)-1-phenylethylamine and used as a catalyst for the enantioselective epoxidation of α,β-enones to afford the corresponding epoxides in good yields and high enantioselectivities at room temperature. 相似文献
12.
A synthesis of a novel electrophilic reagent--β-trifluoroacetylketene diphenyldithioacetal S,S-tetroxide 3 is described. The reaction of 3 with various electron-rich aromatics such as 1,3-dimethoxybenzene, 2-methylthiophene, N-methylpyrrole, and 2-methylindole was investigated. In the course of these reactions an unusual migration of a phenylsulfonyl group takes place. An easy and ready for scale-up procedure for the synthesis of previously unknown β-aryl, α-phenylsulphonyl substituted α,β-unsaturated trifluoromethyl ketones is reported. 相似文献
13.
Kazuishi Makino 《Tetrahedron》2009,65(45):9468-7372
(2S,3R)- and (2R,3R)-2,3-Diaminobutanoic acid (Dab) derivatives were efficiently synthesized from Cbz-(R)-alanine using the proline-catalyzed diastereoselective α-hydrazination reaction and the SmI2-promoted reductive cleavage of the N-N bond as the key steps. 相似文献
14.
Stereocontrolled synthesis of (S)-Fmoc-β-nitroalanine (20) was accomplished from (R)-Fmoc-Ser(tBu)-OH (14) in a total of six steps via an oxime. The oxime (17) was obtained from (R)-Fmoc-Ser(tBu)-H (16), which in turn was obtained by reduction of Weinreb amide (15). Oxidation of oxime was realized with peroxytrifluoroacetic acid at a neutral pH at 0 °C. After removal of the tBu protecting group with 90% TFA/H2O, the hydroxyl group was oxidized with Jones reagent to afford (S)-Fmoc-β-nitroalanine (20) in overall good yield. 相似文献
15.
Yukiyoshi Yamazaki 《Tetrahedron》2008,64(35):8155-8158
A practical synthesis of optically pure PPARα agonist, (R)-K-13675, is described. This process is based on the use of (S)-2-hydroxybutyrolactone, which can be transformed into the requisite n-butyl (S)-2-hydroxybutanoate in an efficient manner. A key reaction is the etherification between the phenol and n-butyl (S)-2-trifluoromethanesulfonyloxybutanoate to give the phenyl ether in excellent yield without loss of optical purity. 相似文献
16.
A straightforward synthesis of enantiopure (S)- and (R)-α-Tfm-pyroglutamic acid is reported. The strategy is based on the use of a chiral CF3-hydroxymorpholinone intermediate conveniently obtained from ethyl trifluoropyruvate-based chiral CF3-oxazolidines (Fox). The key step is an oxidative cyclization followed by a reductive cleavage of the (R)-phenylglycinol chiral auxiliary. 相似文献
17.
Francisco J. Sayago 《Tetrahedron》2009,65(27):5174-5180
High yielding and remarkably selective alkylations of a suitably protected derivative of (2S,3aS,7aS)-octahydroindole-2-carboxylic acid are described. The fused bicyclic structure of this proline analogue greatly influences the stereochemical outcome of direct alkylation reactions taking place at the α-carbon and provides access to α-substituted analogues with retention of the configuration. The overall procedure allows the preparation of enantiopure α-substituted derivatives of this Oic isomer, suitably protected for their incorporation into peptides, in a straightforward manner. 相似文献
18.
Mei Luo 《Tetrahedron letters》2010,51(42):5577-5580
A series of novel N-metal complexes containing chiral α-ethylphenyl amines was synthesized and they catalyzed asymmetric Henry reactions affording products with high enantioselectivity. 相似文献
19.
Xiuyun Yang Yanyan ChengFei Zhao Yunhui LiYuanli Ding Yongjiu LiangFengjiao Gan Dewen Dong 《Tetrahedron》2011,67(43):8343-8347
A facile and efficient synthesis of fully substituted pyridin-2(1H)-ones has been developed by the reaction of readily available α-oxoketene-S,S-acetals with malononitrile in the presence of sodium methoxide in methanol under reflux. 相似文献
20.
Jin-Seong ParkChang-Eun Yeom Soo Hyuk ChoiYong Shik Ahn Sunggu Ro Young Ho Jeon Dong-Kyu Shin B.Moon Kim 《Tetrahedron letters》2003,44(8):1611-1614
An orthogonally protected β,γ′-diamino acid 6 possessing conformationally-constrained ring system was synthesized as a novel cyclic amino acid analogue. This synthesis involves as key steps chemoselective enzymatic hydrolysis of cis-piperidine-3,5-dicarboxylic ester derivative followed by efficient kinetic resolution of the partially resolved half-acid to afford the C1-symmetric piperidine-3,5-dicarboxylic acid monoester in high enantiomeric excess (>98% ee). The optically active half-acid was transformed to the cyclic amino acid via Curtius-type rearrangement. 相似文献