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 31 毫秒
1.
D. Gautam 《Tetrahedron letters》2010,51(32):4199-4201
A stereoselective approach for the synthesis of (+)-(1R,2S,5S,7R)-2-hydroxy-exo-brevicomin from l-ascorbic acid has been described. The key steps are highly stereoselective nucleophilic addition reaction on aldehyde 8 and also a single pot transformation of 15 to (+)-(1R,2S,5S,7R)-2-hydroxy-exo-brevicomin. The later tandem reaction which involves the hydrogenation of double bond, debenzylation, MOM deprotection and bicyclic ketal formation was carried under Pd/C, H2 followed by acid treatment.  相似文献   

2.
Asymmetric syntheses of (1R,1R,5R,7R) and (1S,1R,5R,7R)-1-hydroxy-exo-brevicomins 1 and 2, volatiles of the male mountain pine beetle, and a formal synthesis of (+)-exo-brevicomin 3, a component of the attracting pheromone system of several bark beetles have been achieved. The key steps are Birch reduction of commercially available α-picoline, selective Wittig olefination, and Sharpless asymmetric dihydroxylation.  相似文献   

3.
The syntheses of (2S,3R,4R,5R) and (2S,3R,4R,5S)-1,6-dideoxy-1,6 iminosugars 1a and 1b, respectively, from d-glucose are described. The key transformations in this reaction sequence include regio-selective epoxide ring opening with N-benzylamine followed by intramolecular reductive amination of amino-aldehyde.  相似文献   

4.
Filomena Bellotta 《Tetrahedron》2009,65(18):3659-3663
An efficient and highly stereocontrolled synthesis of (2R,3R,4R,6R)-3-hydroxy-2,4,6-trimethyloctanoic acid, the β-hydroxy acid unit that acylates the N-terminus of homophymine A, has been devised starting from iodoethane and (S,S)-pseudoephedrine propionamide in 9 steps and 36% average overall yield. Comparison of the 1H and 13C NMR and optical rotation data of the resulting β-hydroxy acid with the natural fragment unambiguously verifies the configurational assignment as (2R,3R,4R,6R).  相似文献   

5.
The subsolidus phase relations of R2O3-CaO-CuO ternary systems (R=Nd, Sm, Gd, Tm) have been investigated by X-ray powder diffraction. All samples were synthesized at about 950° in air. There exists a ternary compound Ca14−xRxCu24O41 (x = 4 for R=Nd, Gd and x = 5 for R = Sm) and a ternary solid solution Ca2+xR2−xCu5O10 (R=Nd, Sm, Gd, Tm) with a wide composition range Δx of about 0.6. The compound Ca14−xRxCu24O41 possesses a layered orthorhombic structure and is isostructural to Sr14−xCaxCu24O41. The lattice parameters a and c of the compound are basically independent of the ionic radius of R, while the lattice parameter b and unit-cell volume V decrease substantially with the decrease of the ionic radii of R. The Ca2+xR2−xCu5O10 solid solution is isostructural to Ca2+xY2−xCu5O10, the structure of which is based on an orthorhombic “NaCuO2-type” subcell containing infinite one-dimensional chains of edge-shared square planar cuprate groups crosslinked by the layered cations Ca and R that locate in the inter-chain tunnels.  相似文献   

6.
A convergent synthesis of (4R,15R,16R,21S)-rollicosin (1) and (4R,15S,16S,21S)-rollicosin (2) was accomplished. Hydroxy lactone 6a and/or 6b were synthesized from 4-pentyn-1-ol, and α,β-unsaturated lactone 7 was synthesized from γ-lactone 8 and 5-hexen-1-ol. Inhibitory activity of these compounds was examined with bovine heart mitochondrial complex I.  相似文献   

7.
Yoko Kameda 《Tetrahedron》2006,62(41):9751-9757
(4R,8R)-4,8-Dimethyldecanal, a common aggregation pheromone of Tribolium flour beetles, has been synthesized from (R)-2,3-O-isopropylideneglyceraldehyde in 11 steps and 7% overall yield. The key step in the synthesis is the highly diastereoselective chelation-controlled radical reaction of ethyl (4S,5R)-4-benzyloxy-5,6-(isopropylidenedioxy)-2-methylenehexanoate with ethyl (R)-5-iodo-3-methylpentanoate performed in the presence of 7 equiv of MgBr2·OEt2.  相似文献   

8.
A stereoselective synthesis of (2R,3R) and (2R,3S)-3-hydroxyleucine is disclosed. The key step of the reaction sequence involves, stereo- and regioselective bromohydration of 7, using a brominating agent derived in situ from N-bromosuccinimide and 2,6-lutidine, via intramolecular sulfinyl group participation.  相似文献   

9.
(S,R,S,R,S,R,S)- and (S,R,S,S,S,R,S)-octinaphthalenes were synthesized by oxidative coupling of (S,R,S)-quaternaphthalene, and differences due to axis chirality of (S,R,S,R,S,R,S)-, (S,R,S,S,S,R,S)-, (S,S,S,R,S,S,S)-, and (S,S,S,S,S,S,S)-octinaphthalenes were compared using the Rf values on TLC, specific optical rotations, 1H NMR chemical shifts of the hydroxy groups, and CD spectra. A clear CD additivity was found in the Δ? values of the 1La transition around 290 nm, which are proportional to the difference between the numbers of S and R binaphthalene units.  相似文献   

10.
A highly efficient and stereoselective synthesis of (2R,3R,4R)-HMP is disclosed employing the sulfinyl group as an internal nucleophile to functionalize an olefin in the key step of the reaction sequence. The proline ring is elaborated by a (4C+N) cyclization.  相似文献   

11.
An efficient and stereoselective synthesis of protected (2R,3R,4S)-4,7-diamino-2,3-dihydroxyheptanoic acid, a constituent of the depsipeptides, callipeltins A and D, from d-ribose is described.  相似文献   

12.
Enantioselective oxodiene Diels-Alder reactions catalyzed by (1R,2R)-DPEN-derived triazolium salts were realized successfully. With 0.5 mol % of (1R,2R)-DPEN-derived triazolium salt C and 150 mol % of Et3N, the reactions of various α-chloroaldehydes (α-bromoaldehyde) with substituted enones led to 3,4-dihydropyridinones and their derivatives in good yields, diastereoselectivities, and enantioselectivities (up to 97% ee).  相似文献   

13.
A concise and highly efficient synthesis of l-arabino-[2R,3S,4R] and l-xylo-[2R,3S,4S]-C18-phytosphingosines has been achieved. The synthetic strategy features the Sharpless kinetic resolution and tethered aminohydroxylation as the key steps.  相似文献   

14.
Stereoselective synthesis of cruciferous indole phytoalexin (R)-(+)-1-methoxyspirobrassinin and its unnatural (S)-(−)-enantiomer was achieved by spirocyclization of 1-methoxybrassinin in the presence of (+)- and (−)-menthol and subsequent oxidation of the obtained menthyl ethers. Methanolysis of menthyl ethers in the presence of TFA afforded (2R,3R)-(−)-1-methoxyspirobrassinol methyl ether as well its unnatural (2S,3S)-, (2R,3S)-, and (2S,3R)-isomers.  相似文献   

15.
A stereoselective synthesis of the pentaketide lactone (3R,4S,5S,9S)-3,5,9-trihydroxy-4-methylundecanoic acid δ-lactone has been achieved.  相似文献   

16.
The crystal chemistry and crystallography of the compounds SrR2CuO5 (Sr-121, R=lanthanides) were investigated using the powder X-ray Rietveld refinement technique. Among the 11 compositions studied, only R=Dy and Ho formed the stable SrR2CuO5 phase. SrR2CuO5 was found to be isostructural with the “green phase”, BaR2CuO5. The basic structure is orthorhombic with space group Pnma. The lattice parameters for SrDyCuO5 are a=12.08080(6) Å, b=5.60421(2) Å, c=7.12971(3) Å, V=482.705(4) Å3, and Z=8; and for the Ho analog are a=12.03727(12) Å, b=5.58947(7) Å, c=7.10169(7) Å, V=477.816(9) Å3, and Z=8. In the SrR2CuO5 structure, each R is surrounded by seven oxygen atoms, forming a monocapped trigonal prism (RO7). The isolated CuO5 group forms a distorted square pyramid. Consecutive layers of prisms are stacked in the b-direction. Bond valence calculations imply that residual strain is largely responsible for the narrow stability of the SrR2CuO5 phases with R=Dy and Ho only. X-ray powder reference diffraction patterns for SrDy2CuO5 and SrHo2CuO5 were determined.  相似文献   

17.
A stereoselective approach for the total synthesis of lactone (5R,7R,9R)-7,9-dihydroxy-5-decanolide is described. The sequence of synthetic reactions involves a Keck asymmetric allylation, diastereoselective iodo-carbonate cyclization, regioselective ring-opening reaction, oxidative lactonization.  相似文献   

18.
A novel dichloro zinc complex (L1)ZnCl2, where L1 is N,N′-bis-(2,6-dichloro-benzyl)-(R,R)-1,2-diaminocyclohexane, has been synthesized and characterized. The dimethyl derivatives, generated in situ from the well characterized dichloro zinc complexes (L1)ZnCl2 and (L2)ZnCl2, where L2 is N,N′-bis-(benzyl)-(R,R)-1,2-diaminocyclohexane, were employed as initiators for the ring opening polymerization (ROP) of rac-lactide (rac-LA). The complexes were found to be highly efficient initiators yielding the polylactide (PLA) with a narrow molecular weight distribution. The catalytic activity and heterotactic selectivity of the Zn(II) complexes were affected by the substituents on the phenyl groups of benzyl moieties in (R,R)-1,2-diaminocyclohexane. The dimethyl derivative of (L2)ZnCl2 produced highly stereocontrolled PLA with Pr = 0.75 at −25 °C.  相似文献   

19.
The synthesis of (1R, 2S, 3R) and (1S, 2S, 3R)-2-(N-benzoylamino)-1-(2-furyl)-1, 3-butandiols (15) and (16) from D-threonine is described. The assignment of absolute configuration of the newly formed asymmetric center at C-1 was based on the 1H-NMR spectra of O-isopropylidene derivatives 17 and 18.  相似文献   

20.
The synthesis of (4R,8R)- and (4S,8R)-4,8-dimethyldecanal 1 and 1a has been achieved connecting the chiral building block (R)-2-methyl-1-bromobutane 4 with (R)- and (S)-citronellol derivatives. The key intermediate 4 was obtained optically pure in five steps from methyl (S)-3-hydroxy-2-methylpropionate 2.  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