首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
Abstract

Ferrier glycosylation could be employed for the syntheses of a range of unsaturated O- as well as S-glycopeptides. Thus, featuring high yields and in many cases convincing diastereomeric excesses, an efficient protocol for formation of this class of compounds was established.  相似文献   

2.
A self-intermolecular cyclocondensation reaction of 3,4-dihydropyrimidine-2-thione(DHPM) to give a novel tricyclic structure containing DHPM core in the presence of diethyl azodicarboxylate(DEAD) and triphenylphosphine(TPP) at room temperature is reported.  相似文献   

3.
A 1,4 OO silyl migration followed by nucleophilic substitution with phthalimide was observed under Mitsunobu reaction conditions. This one step secondary alcohol protection and primary alcohol substitution with N-nucleophiles was extended to a variety of 2-hydroxyethyl trialkylsilylether derivatives. A possible mechanism has been postulated based on the pKa values of the alcohol and nucleophile. The present one-pot silyl migration and substitution reaction might find application in the stereoselective synthesis of novel iminosugar derived anti diabetic agents.  相似文献   

4.
5.
Tayama E  Isaka W 《Organic letters》2006,8(24):5437-5439
The Ferrier reaction of O-1,3-dienyl acetals promoted by organoaluminum complexes such as methylaluminum bis(2,6-di-tert-butyl-4-methylphenoxide) (MAD) is shown to proceed with a high degree of regio- and stereoselectivity to afford the corresponding alpha-alkenyl-substituted beta-alkoxy aldehydes in good yields. The mechanistic origin of the high regiocontrolling ability of MAD is elucidated. This method, coupled with the easy availability of the requisite substrates, expands the synthetic scope of the Ferrier reaction. [reaction: see text].  相似文献   

6.
A single step procedure for the direct and regioselective synthesis of carbohydrate azides from unprotected sugars using hydrazoic acid under Mitsunobu conditions is reported. A series of mono-, di-, or triazido polyhydroxylated systems are described.  相似文献   

7.
8.
Amino acid 2,3-unsaturated glycopyranosyls have been prepared by the Ferrier rearrangement of acetyl protected glucals and PEG-bound amino acids in the presence of a catalytic quantity of BF3·Et2O in CH2Cl2 at ambient temperature.  相似文献   

9.
Treatment of propargylic dithiolanes 1 with (n)BuLi followed by a carbonyl electrophile yields the corresponding homopropargylic alcohol 3. Upon treatment with 2 equiv of PPh3 and DIAD, elimination of SR and OH moieties from 3 affords the corresponding olefins 4 in moderate to good yield. The reaction can be considered an alternative of McMurry coupling of two different carbonyl equivalents.  相似文献   

10.
Regiochemical control in the functionalization of ambident nucleophiles is of particular interest in organic chemistry. Herein, we demonstrate that O-alkylation of ambident 3-hydroxyisoxazoles, which are heterocyclic bioisosteres of carboxylic acids, predominates under Mitsunobu conditions. In several cases, excellent O-regioselectivity (?95%) was observed. It is noteworthy that reactions were complete within 15 min at room temperature. Furthermore, the conditions are compatible with a range of alcohols that cover all of the typical protecting groups for the 3-hydroxyisoxazole motif, providing milder, simpler and less hazardous protocols to those commonly followed in the literature.  相似文献   

11.
The carboxyl group of a N-acylated amino acid may be protected by conversion to an oxazole derivative which, on photoxygenation, regenerates the carboxyl group in activated (triamide) form for peptide synthesis.  相似文献   

12.
A four-step synthesis of (-)-lentiginosine and its epimers is described starting from 2-bromopyridine. The key step consisted of a quaternarization of a fully unprotected pyridinium-polyol unit using Mitsunobu methodology. Subsequent PtO(2)-catalyzed diastereoselective hydrogenation of the pyridinium ring proceeded smoothly and led to the expected dihydroxyindolizidines with excellent yields. This stereochemically flexible strategy has been illustrated by the concise total synthesis of non-natural products derivatives such as (-)-lentiginosine and its stereoisomers in high yields.  相似文献   

13.
Tarun Kanti Pradhan 《Tetrahedron》2004,60(24):5215-5224
A short and efficient synthesis of condensed 1,4-oxathiin-2-ones from easily available phenols is described. The key step in this synthesis is a hitherto unreported anionic rearrangement under directed metalation conditions. The rearrangement occurs after side chain deprotonation of a methyl sulfanyl group by an O-carbamate directed metalating group and the reaction mixture is kept at room temperature for 8-12 h. Acid-mediated cyclisation of the rearranged product affords [1,4]oxathiin-2-one.  相似文献   

14.
An improved method for the synthesis of 2,3-unsaturated-O-glycosides has been developed. ZnCl2 impregnated on activated alumina acts as an excellent reagent system for the conversion of 2,4,6-tri-O-acetyl-d-glucal to 2,3-unsaturated-O-glycosides with high α-selectivity.  相似文献   

15.
《Tetrahedron letters》1986,27(30):3521-3524
A general method has been developed for nearly quantitative synthesis of N-benzylporphyrins by use of benzyldiphenylsulfonium tetrafluoroborate. The N-benzylporphyrins (including natural, synthetic, water soluble and non-water soluble porphyrins) insert Cu(II), Co(II), Pd(II) and Ni(II) rapidly and then readily lose the N-benzyl group to give non-N-substituted metalloporphyrins. The reactions of Cu(II), Co(II) and Pd(II) are efficient under mild conditions compatible with biological preparations.  相似文献   

16.
《Tetrahedron: Asymmetry》2000,11(17):3619-3634
Mexiletine [1-(2,6-dimethylphenoxy)-2-propanamine], a chiral, orally effective antiarrhythmic agent, and several analogues substituted on either the stereogenic centre or the xylyloxy moiety, were prepared in both, highly enriched, optically active forms. According to the ‘chiral pool’ approach, the appropriate amino alcohols, protected as the corresponding phthalimide derivatives, were condensed with the desired phenols under either Mitsunobu (method A) or Williamson (method B) conditions. Generally, method A provided the most efficient route, both in terms of yields and number of steps necessary. Only when an isopropyl group was present on the stereogenic centre, i.e. when 2-amino-3-methylbutanol was used as the starting alcohol, method B proved to be the only available route, method A giving no product other than the starting phthalimide derivative. Regardless of the method used, enantiomeric excesses ranged from 91 to 99%. Given the availability of both variously substituted phenols and optically active amino alcohols, the two methods described herein, taken together, may serve as a versatile approach, useful to meet the needs of new chiral, optically active mexiletine analogues, possibly endowed with higher potency in exerting a use-dependent block on sodium channels and/or more resistant to biotransformations.  相似文献   

17.
Because of the peculiar reactivity of the idose part of N-Boc neomycin B , special care must be exercised to introduce a substituent at the 5"-position of the antibiotic when using Mitsunobu reaction conditions.  相似文献   

18.
Nucleoside analogues 9 and 12 were obtained in good yields from alcohol 7 which, under Mitsunobu conditions, led to the title products after deprotection steps.  相似文献   

19.
Here, we report a formal synthesis of the marine cytotoxic meroterpenoid actinoranone. Key steps include a semipinacol rearrangement/Wittig reaction sequence and a chiral pool approach for the syntheses of the tetralone and the ocatalin fragments, respectively. The presented route provides access to the natural product in 14 steps in the longest linear sequence.  相似文献   

20.
Using the Mitsunobu reaction as a key step, a general and efficient method for the synthesis of EDOT monomers has been developed. Novel substituted EDOTs and the first chiral derivatives were generated in high yields.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号