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1.
The use of several chiral trifluoromethylated building blocks 1a, 1b, 9a and 9b was attempted to synthesize of syn-(3-trifluoromethyl)cysteine. A novel and efficient enantioselective synthesis of both enantiomers of syn-(3-trifluoromethyl)cysteine derivatives 12a and 12b was successfully achieved. 相似文献
2.
《Tetrahedron: Asymmetry》2007,18(6):787-790
Both enantiomers of 6-methyl-ε-caprolactone (6-MeCL) are obtained in high enantiomeric excess by the combination of an enzymatic ring opening of racemic 6-methyl-ε-caprolactone and subsequent enzymatic ring closure. Immobilized Candida antarctica lipase B (Novozym 435) was selected as the biocatalyst for both the ring-opening and the ring-closing reaction. This route provides ready access to enantiopure (S)-6-MeCL (ee = 99.6%) and (R)-6-MeCL (ee = 98.8%). 相似文献
3.
The stereoselective acetylation of meso-2,2-dimethyl-1,3-cyclohexanediol by vinyl acetate in the presence of three lipases gave the (1R,3S)-monoester in high enantiomeric excess (ee > or = 98%). The hydrolysis of the corresponding meso-diacetate in the presence of Candida antarctica lipase in phosphate buffer provided the opposite enantiomer. Optically active monoacetates were converted to both enantiomers of 3-hydroxy-2,2-dimethylcyclohexanone, a versatile chiral building block. 相似文献
4.
Annamaria Varga Valentin Zaharia Mihály Nógrádi László Poppe 《Tetrahedron: Asymmetry》2013,24(21-22):1389-1394
Ethyl (S)-3-hydroxy-3-phenylpropionate (S)-2 was obtained by the asymmetric reduction of ethyl 3-phenyl-3-oxopropionate 1 with the yeast Saccharomyces cerevisiae (ATCC 9080). The kinetic resolution of racemic ethyl 2-acetoxy-3-phenyl-propionate rac-3 with the same microorganism, gave after hydrolysis ethyl (R)- and (S)-3-hydroxy-3-phenylpropionates (R)-2 and (S)-2 which were converted by a straightforward series of reactions to the enantiomers of 3-amino-3-phenyl-propionic acids (S)-6 and (R)-6. The asymmetric reduction and hydrolytic kinetic resolution were also tested with several other whole cell systems under a variety of conditions. 相似文献
5.
Both the enantiomers of trans-3-hydroxypipecolic acid have been synthesized employing the Sharpless asymmetric dihydroxylation and epoxidation as the key steps starting from a commercially available starting material 1,4-butanediol. 相似文献
6.
An efficient synthesis of 2-bromo-3-aryloxybenzothiophene derivatives by a conjugate addition-elimination sequence of 2,3-dibromo benzothiophene dioxides with phenolic nucleophiles has been developed. These benzothiophene derivatives serve as important intermediates for the synthesis of SERM analogues. 相似文献
7.
Based on the lipase-catalysed kinetic resolution of the silyloxyalcohol (1RS,2SR)-5 by transesterification with vinyl acetate in the presence of lipase from Pseudomonas cepacia a synthesis of both enantiomers of the β-amino acid cispentacin (1R,2S)-1 and (1S,2R)-1 using simple functional group interconversions is described. 相似文献
8.
Gowrisankar Reddipalli Mallam Venkataiah Nitin W. Fadnavis 《Tetrahedron: Asymmetry》2010,21(3):320-324
The synthesis of both the (R)- and (S)-enantiomers of the natural product rugulactone has been achieved. Candida rugosa lipase hydrolyzes the butyrate ester of the protected 3-hydroxy homoallylic alcohol with very high enantioselectivity (E = 244) and provides the key intermediates with high enantiomeric purity (ee 98–99%) and excellent yields. 相似文献
9.
The stereoselective total synthesis of both enantiomers of rugulactone 1 has been completed by applying enantioselective allyl additions as key steps. Two different strategies based on highly stable and enantiomerically pure α-substituted allylboronic esters 2 and 3 were performed starting from boronic ester 4. 相似文献
10.
Kündig EP Cannas R Laxmisha M Ronggang L Tchertchian S 《Journal of the American Chemical Society》2003,125(19):5642-5643
Both enantiomers of acetoxytubipofuran were synthesized using enantioselective and diastereoselective dearomatization sequences starting from the benzaldehyde chromium tricarbonyl complex. Following aldol condensation, a sequence involving Pd-catalyzed allylic substitution was used in the synthesis of the (-)-enantiomer, whereas the (+)-enantiomer was reached via an Eschenmoser-Claisen rearrangement. Chiroptical data show that a revision of the previously assigned absolute configuration of the natural product is required. 相似文献
11.
A stereocontrolled total synthesis of both the (+)- and (-)-epolactaene ((+)- and (-)-1) enantiomers from tetrahydropyran-2-ol is described. The following reactions in this synthesis are particularly noteworthy: (1) the stereoselective construction of the conjugated (E,E,E)-triene by a combination of kinetic deprotonation and thermodynamic equilibration, (2) the E-selective Knoevenagel condensation of beta-ketonitrile 33 with a chiral 2-alkoxyaldehyde, (3) a diastereoselective epoxidation achieved using a bulky nucleophile (TrOOLi) and an appropriate protecting group, (4) the mild hydrolysis of an alpha-epoxy nitrile by silica gel on TLC facilitated by hydroxyl-mediated, intramolecular assistance. 相似文献
12.
We have achieved the first asymmetric synthesis of (+)- and (−)-andirolactone. The key steps were separation of limonene oxide diastereomers, asymmetric oxidation induced by the chiral intermediate and ring-closing metathesis in the presence of catalytic amounts of Lewis acid to form the spirocyclic butenolides. 相似文献
13.
14.
《Tetrahedron: Asymmetry》2003,14(11):1489-1493
4-Oxo-3,4-dihydro-2-chromen-3-yl acetate is synthesized using manganese(III)acetate starting from 2,3-dihydro-4H-chromen-4-one. K2CO3 mediated hydrolysis of 4-oxo-3,4-dihdro-2-chromen-3-yl acetate furnished 3-hydroxy-2,3-dihydro-4H-chromen-4-one in high yield.The enantioselective hydrolysis of (±)-4-oxo-3,4-dihydro-2-chromen-3-yl acetate in various organic solvent-phosphate buffer (pH7) systems and enantioselective transesterification of (±)-3-hydroxy-2,3-dihydro-4H-chromen-4-one in organic solvents was investigated by screening a range of lipases. The lipase Amano PS, PPL, PLE and CCL-catalyzed asymmetric ester hydrolysis and transesterification afforded the enantiomers of 3-hydroxy-2,3-dihydro-4H-chromen-4-one and 4-oxo-3,4-dihydro-2-chromen-3-yl acetate with high enantiomeric excess (up to 97% ee) and in good yields. 相似文献
15.
François-René Alexandre Amaya BerecibarRoger Wrigglesworth Thierry Besson 《Tetrahedron letters》2003,44(24):4455-4458
An original route to the rare 8H-thiazolo[5,4-f]quinazolin-9-one 1 and the novel 7H-thiazolo[4,5-h]quinazolin-6-one 2 is described. Access to the regioisomers was realized by fusion of a thiazole and a quinazoline ring via Appel's salt chemistry. Thermal reactions were carried out using a focused microwave reactor, reducing the overall time of the multi-step synthesis. 相似文献
16.
Enantiodivergent synthesis of both (-)- and (+)-disparlure, a bioactive pheromone, possessing a cis-epoxide has been accomplished. The key step involves the cross metathesis of a chiral homoallylic alcohol derived from l-(+)-tartaric acid. 相似文献
17.
Both enantiomers of the polyketide-derived lactone citreofuran (4) have been prepared. The enantiopure building blocks were obtained on a chemoenzymatic route ((S)-6) and by a chiral pool synthesis ((R)-6). The crucial step in the synthesis, a macrolactonization, was accomplished under Mitsunobu conditions. 相似文献
18.
A novel modular and practical methodology for preparation of 6-substituted pyridin-3-yl C-nucleosides was developed. The Heck reaction of 2-chloro-5-iodopyridine with a 3'-TBDMS-protected glycal gave a 6-chloropyridin-3-yl nucleoside analogue, which was then desilylated, selectively reduced, and reprotected to give the TBDMS-protected 6-chloropyridin-3-yl C-2'-deoxyribonucleoside as a pure beta-anomer in a total yield of 39% over four steps. This key intermediate was then subjected to a series of palladium-catalyzed cross-coupling reactions, aminations, and alkoxylations to give a series of protected 1beta-(6-alkyl-, 6-aryl-, 6-hetaryl, 6-amino-, and 6-tert-butoxypyridin-3-yl)-2'-deoxyribonucleosides. 6-Unsubstituted pyridin-3-yl C-nucleoside was prepared by catalytic hydrogenation of the chloro derivative and 6-oxopyridine C-nucleoside by treatment of the 6-tert-butoxy derivative with TFA. Deprotection of all the silylated nucleosides by Et3N.3HF gave a series of free C-nucleosides (10 examples). 相似文献
19.
Steven M Allin Guy B Streetley Stella L James William P Martin 《Tetrahedron letters》2004,45(28):5493-5496
A formal asymmetric synthesis of both enantiomers of the Erythrina alkaloid 3-demethoxyerythratidinone is reported through the application of a highly functionalised lactam template as an N-acyliminium precursor. 相似文献
20.
《Tetrahedron: Asymmetry》1998,9(16):2827-2831
The stereoselective acetylation of meso-2,3-bis(3,4-dimethoxybenzyl)butanediol by vinyl acetate in the presence of Candida antarctica lipase in benzene gave the corresponding (+)-(2S,3R) monoester (ee ≥98%). Transesterification of meso-2,3-bis(3,4-dimethoxybenzyl)butyl diacetate, in the presence of the same enzyme, by ethanol in benzene/isopropyl ether gave the corresponding (−)-(2R,3S) monoester (ee ≥98%). Both enantiomers of the known cis-2,3-bis(3,4-dimethoxybenzyl)butyrolactone were synthesized from these monoesters. 相似文献