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1.
《Tetrahedron: Asymmetry》2000,11(23):4681-4686
A short and efficient synthesis of the title compounds is described. (S)-(−)-β-Cuparenone was prepared in 31% yield from p-tolualdehyde and mesityl oxide in eight steps. Absolute stereochemistry was established by means of a diastereoselective cyclopropanation using (R,R)-hydrobenzoin as a recoverable auxiliary. 相似文献
2.
Abstract (R)-(?)-β-Cuparenone has been synthesized from (S)-(+)-acid-2 obtained via resolution of the racemic acid. Two of the noteworthy steps are (a) repeated methylation of ester (+)-8 with LDA/MeI to furnish (+)-10 and (b) the reaction of 12, having two neopentyl units with NaCN. 相似文献
3.
《Tetrahedron: Asymmetry》1999,10(22):4281-4284
A short and efficient synthesis of the unnatural enantiomer of (+)-(S)-ipsdienol 1 and (−)-(S)-ipsenol 2 is presented via an asymmetric allylboration. The synthesis was achieved by using a one-pot reduction–methylenation of an exo-methylene lactone intermediate. 相似文献
4.
The structure of (+)-β-turmerone ((+)- 1a ), a constituent of the rhizomes of Curcuma longa Linn. , and Curcuma xanthorriza, is established as (1′R,6S)-2-methyl-6-(4′-methylenecyclohex-2′-en-1′-yl)hept-2-en-4-one by synthesis of its enantiomer (−)- 1a , and of the corresponding (1′S,6S)-diastereoisomer (+)- 1b as well. In a stereospecific seventeen-step procedure, the monoterpene diols 2a and 2b of well-established configuration are converted into the target compounds (−)- 1a and (+)- 1b , respectively. Moreover, (−)-bisacurol (−)- 3a (II), the enantiomer of another bisabolane sesquiterpene derived from Curcuma xanthorriza, is obtained as a single stereoisomer and shown to be (1′S,6R)-2-methyl-6-(4′-methylenecyclohex-2′-en-1′-yl)hept-2-en-4-ol, the relative configuration at the remaining OH-substituted chiral center C(4) still being unknown. 相似文献
5.
Stephen G. Davies Ai M. Fletcher Linlu Lv Paul M. Roberts James E. Thomson 《Tetrahedron letters》2012,53(24):3052-3055
The asymmetric synthesis of (?)-(R)-sitagliptin was achieved in seven steps from commercially available starting materials using the highly diastereoselective conjugate additions of either lithium (R)-N-benzyl-N-(α-methylbenzyl)amide or lithium (R)-N-benzyl-N-(α-methyl-p-methoxybenzyl)amide to tert-butyl 4-(2′,4′,5′-trifluorophenyl)but-2-enoate to install the correct stereochemistry. Subsequent sequential acid-catalysed hydrolysis of the resultant β-amino esters, HOBt/EDC mediated coupling with the triazolopyrazine fragment, and hydrogenolysis gave (?)-(R)-sitagliptin in 43% and 42% overall yields, respectively. 相似文献
6.
A novel, efficient and protecting group free enantioselective synthetic approach of (?)-(R)-1 and (+)-(S)-rolipram 2 is described employing the organocatalyzed asymmetric Michael addition, Henry condensation, Wittig olefination and reductive lactamization reactions as key steps. 相似文献
7.
《Tetrahedron: Asymmetry》1999,10(11):2113-2118
In this report we describe an efficient synthesis of (R)-(−)-baclofen, a selective GABAB agonist used as an antispastic agent. Our strategy is based on an enantioselective deprotonation of a cyclobutanone easily obtained by [2+2] cycloaddition of 4-chlorostyrene and dichloroketene. 相似文献
8.
Virginia M. Mastranzo José Luis Olivares Romero Francisco Yuste Benjamín Ortiz Rubén Sánchez-Obregón José L. García Ruano 《Tetrahedron》2012,68(4):1266-1271
(S)-(?)-Tetrahydropalmatine 2 and (S)-(?)-canadine 4 were synthesized in three steps from (S)-6, in 33% and 34% overall yield, respectively. Thus, condensation of the (S)-(E)-sulfinylimines 10 and 11 with the carbanion derived from (S)-6 gave the tetrahydroisoquinolines 12 and 13, respectively, which upon TFA induced N-desulfinylation, and subsequent microwave assisted Pictet–Spengler cyclization effected both cyclization and C-desulfinylation producing (S)-(?)-tetrahydropalmatine 2 and (S)-(?)-canadine 4 in optically pure form. 相似文献
9.
《Tetrahedron: Asymmetry》2001,12(17):2385-2387
A total synthesis of (S)-(−)-acromelobinic acid 2, which was isolated from clitocybe acromelalga, was achieved via an asymmetric hydrogenation protocol. Dehydroamino acid derivative 12 was prepared from 2,5-lutidine 5 and subjected to asymmetric hydrogenation using (S,S)-[Rh(Et-DuPHOS)(COD)]BF4 to give the (S)-(+)-pyridylalanine derivative 13 in 93% yield and >96% e.e. Removal of the protecting groups in (S)-(+)-13 afforded (S)-(−)-acromelobinic acid 2. 相似文献
10.
《Tetrahedron: Asymmetry》2000,11(15):3063-3068
A convergent synthesis of (S)-(−)-3-(2-carboxy-4-pyrrolyl)-alanine (CPA) 1, a non-proteinogenic amino acid is described starting from a commercially available dimethyl l-aspartate 2 in good overall yield. 相似文献
11.
12.
《Tetrahedron: Asymmetry》2000,11(18):3665-3669
An efficient synthesis of the (S)-(−)- and (R)-(+)-enantiomers of 15-deoxyspergualin (15-DSG) is reported. The synthesis involves preparative HPLC separation and subsequent hydrogenolysis of two diastereoisomers 10a and 10b of fully protected 15-DSG penultimates. Alternatively, diastereomerically pure amide 10b (97% de) was also prepared from acid 8b (97% de), which was obtained via crystallization of a 1:1 diastereomeric mixture of 8a and 8b. 相似文献
13.
Eudesmanederivativeshavebeendrawingconsiderableattentionduetotheirwidespectrumofbiologicalproperties,particularlyantifeedant,cellgroWthinhibitoryandplantgroWthregulatingactivitiesl'2.Recently,twoepimericeudesmanederivatives( )-5a-hydroxy-6-selinene1and(-)-56-hydroxy-6-selinene2wereisolated3fromtheaerialpartsofCSubtraPicaFMell.,andtheirstructuresweredeterminedbyspectroscopicmethods.Herein,wereportafacilesynthesisofbothtwodiastereomers1and2from( )-dihydrocarvone3infivesteps,usingtheregioselect… 相似文献
14.
《Tetrahedron: Asymmetry》2004,15(17):2657-2660
In the presence of 10% NaOH in boiling MeOH enantiomerically enriched HPPH is racemized. This permits the deracemization of HPPH in the presence of brucine, giving enantiomerically pure (−)-(S)-HPPH [(−)-(S)-5-(4-hydroxyphenyl)-5-phenylhydandoin]. 相似文献
15.
《Tetrahedron: Asymmetry》1998,9(9):1525-1530
A concise and efficient synthesis of (−)-10-epi-5β,11-dihydroxyeudesmane 1 and (−)-4,10-epi-5β,11-dihydroxyeudesmane 2, via (−)-10-epi-γ-eudesmol 5, was accomplished starting from (+)-dihydrocarvone. The salient feature of our synthesis is the utilization of substrate-directable epoxidation and homogeneous hydrogenation to control the stereochemistry at the C-4 and C-5 positions of the title compounds. 相似文献
16.
《Tetrahedron: Asymmetry》2003,14(3):363-366
Condensation of pyruvate and acrolein with whole cells of baker's yeast resulted in a mixture of 3-hydroxy-1-penten-4-one 1 and 4-hydroxy-1-penten-3-one 2. The absolute configuration (R) and the enantiomeric excess (ee 72%) of the compound 1 were determined. 相似文献
17.
18.
《Tetrahedron: Asymmetry》2000,11(20):4221-4225
The resolution of the 4-acetyl[2.2]paracyclophane by the SAMP-hydrazone method is described. A new, short, high yield synthesis of both enantiomers (S)-(+)- and (R)-(−)-4-ethenyl[2.2]paracyclophane is reported. 相似文献
19.
《Tetrahedron: Asymmetry》1999,10(22):4349-4356
An asymmetric synthesis of (R)-(−)-mevalonolactone is described using the Sharpless asymmetric dihydroxylation and the regioselective nucleophilic opening of a cyclic sulfate as key steps. 相似文献
20.
Stephen G. Davies Ai M. Fletcher Clément Lebée Paul M. Roberts James E. Thomson Jingda Yin 《Tetrahedron》2013,69(4):1369-1377
The most efficient and concise asymmetric synthesis of (?)-(1R,7aS)-absouline to date, which was accomplished in eight steps and 20% overall yield from commercially available starting materials, is described. The doubly diastereoselective conjugate addition of lithium (S)-N-benzyl-N-(α-methylbenzyl)-amide to an enantiopure α,β-unsaturated ester derived from l-proline was employed as the key step. Subsequent hydrogenolytic N-debenzylation and acid-promoted cyclisation of the resultant β-amino ester produced the 1-aminopyrrolizidin-3-one scaffold, then reduction with DIBAL-H was followed by DCC-mediated coupling with (E)-p-methoxycinnamic acid to complete the synthesis of (?)-(1R,7aS)-absouline. 相似文献