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1.
Asymmetric synthesis of β-lactams by the [2+2] cycloaddition of ketenes with chiral imines derived from d-(+)-glucose was carried out; predominantly cis-β-lactams were formed with very high diastereoselectivity. The stereochemistry at C-3 and C-4 was established as 3S and 4R from the known absolute configuration of the sugar moiety.  相似文献   

2.
《Tetrahedron: Asymmetry》1999,10(7):1315-1322
The synthesis of both cis- and trans-crobarbatic acid is reported. The five-step sequence proceeds in high yield and with control of both relative and absolute stereochemistry. The key step in the synthesis is the Birch reductive alkylation of a chiral furoic acid which sets the absolute stereochemistry of the products. The stereochemistry of the compounds described was proven unambiguously by X-ray crystallography on one synthetic intermediate and on trans-crobarbatic acid.  相似文献   

3.
Cyano-functionalized allylic phosphine substrates containing the ortho-metalated (R)-(1-(dimethylamino)ethyl)naphthalene as the chiral auxiliary were synthesized from bromoacetaldehyde dimethylacetal via a one-pot process. The diastereoselective hydrophosphination reactions of the cis- and trans-allylic phosphine substrates gave the cyano-functionalized chiral 1,2-bis(diphenylphosphino)ethane products with high yield and stereoselectivity. The subsequent organic transformation reactions of the cyano-substituted products chemoselectively afforded the formyl- and hydroxyl-functionalized chiral 1,2-diphosphine complexes with retention of stereochemistry. The coordination properties and absolute configurations of the novel 1,2-diphosphine complexes were established by single crystal X-ray crystallography. The optically pure 1,2-bis(diphenylphosphino)ethane ligands with cyano-, formyl- and hydroxyl-functionalities could be liberated in high yields from the corresponding dihalo palladium complexes by treatment with aqueous potassium cyanide.  相似文献   

4.
《Tetrahedron: Asymmetry》2007,18(4):547-551
The determination of the absolute stereochemistry of hydroxy fatty acid methyl esters as their (S)-ibuprofen esters is possible via standard gas chromatographic techniques. Analyses of various racemic and nonracemic standards and mixtures from enzymic oxidation show excellent resolution of the resultant diastereomers, with the (S,S)-diastereomers eluting first in all cases studied. The stereochemistry of the oxidation of dodecanoic acid by P450BM3, which has not been previously reported, was determined by this method and indicated a preference for (R)-hydroxylation. The sensitivity of this technique allows the analysis of very small quantities of product, which has revealed that the oxidation of dodecanoic and hexadecanoic acids by the T268A mutant of P450BM3 display the same stereochemical efficiency and produce (R)-hydroxy fatty acids in the same manner as wildtype P450BM3, despite the poor coupling efficiency of these substrates. This stereochemistry implies that hydroxylation catalysed by the T268A mutant of P450BM3 occurs through residual levels of the normal hydroxylating species.  相似文献   

5.
9,10-Dicyanoanthracene (DCA) sensitizes the electron-transfer photo-oxygenation of epoxides in oxygen-saturated acetonitrile to form ozonides. Epoxides with oxidation potentials lower than 2 V vs SCE quench the fluorescence of DCA and are converted to the ozonides with DCA alone. Epoxides which do not quench the singlet excited state of DCA are unreactive under these conditions. However, the photo-oxygenation of these epoxides can be effected by addition of biphenyl (BP) as a catalyst or co-sensitizer. Investigations of the stereochemistry of the reactions of cis- and trans-2,3-diaryloxiranes has shown that both isomeric epoxides are converted exclusively to the corresponding cis-ozonides. Co-sensitized photo-oxygenation of cis- and trans-2,3-diphenyloxirane affords only cis-3,5-diphenyl-1,2,4-trioxolane. The same stereochemical course is followed for the electron-transfer photo-oxygenation of more easily oxidized 2,3-dinaphthyloxiranes that do not require BP co-sensitization. The stereochemistry of the naphthyl-substituted ozonides has been unequivocably assigned by an X-ray structure of cis-3,5-bis(2'-naphthyl)-1,2,4-trioxolane. The corresponding trans-ozonide was prepared by ozonation of cis-1,2-bis(2'-naphthyl)ethene and stereochemically identified by Chromatographic resolution using high-performance liquid chromatography with optically active (+)-poly(triphenylmethyl methacrylate) as the stationary phase. These stereochemical results have been interpreted in terms of a mechanism involving addition of singlet oxygen as a dipolarophile to intermediate carbonyl ylides.  相似文献   

6.
The total synthesis of two decahydroquinoline poison frog alkaloids ent-cis-195A and cis-211A were achieved in 16 steps (38% overall yield) and 19 steps (31% overall yield), respectively, starting from known compound 1. Both alkaloids were synthesized from the common key intermediate 11 in a divergent fashion, and the absolute stereochemistry of natural cis-211A was determined to be 2R, 4aR, 5R, 6S, and 8aS. Interestingly, the absolute configuration of the parent decahydroquinoline nuclei of cis-211A was the mirror image of that of cis-195A, although both alkaloids were isolated from the same poison frog species, Oophaga (Dendrobates) pumilio, from Panama.  相似文献   

7.
《Tetrahedron letters》1987,28(50):6391-6392
The absolute stereochemistry of the 4-bromo-cis-2,3-dihydroxycyclohexa-4,6-diene-1-carboxylic acid, one of a series of diols produced by P. putida strain JT 107, was shown by X-ray crystal analysis to be (2-R, 3-R).  相似文献   

8.
The photochemistry of the stereoisomeric 1,3-dimethyl-3(2-phenylethenyl)cyclohexenes has been explored Direct irradiation of the cis- and trans-β-styrylcyclohexenes leads to di-π-methane rearrangement, producing the endo- and exo-3,7-dimethyl-8-phenybicyclo[5.1.0]oct-2-enes, and cis -trans isomerization, interconverting the 1,4-diene containing substrates. Triplet sensitized photolysis of both substituted cyclohexenes leads exclusively to cis-trans isomerization. Results from low conversion direct irradiations of the cis- and trans-β-styrylcyclohexenes indicate that the singlet rearrangements are stereospecific, and lead to formation of the 8-exo and 8-endo-phenylbicyclic octenes, respectively. The relationship between di-π-methane structure and triplet reaction efficiency, and the effect of conformation on the rearrangement stereochemistry are discussed.  相似文献   

9.
We report a synthesis of a single enantiomer of a mycolic acid from Mycobacterium tuberculosis containing a di-cis-cyclopropane. The method can be simply varied to modify the chain lengths or the absolute stereochemistry of either cyclopropane.  相似文献   

10.
《Tetrahedron: Asymmetry》2003,14(13):1935-1942
The absolute configuration of Etzionin, a marine peptide-like compound isolated in 1989 from a red tunicate collected from the Red Sea has been determined by a combination of synthetic and spectroscopic procedures. Finally, its absolute stereochemistry has been established as 3S,3′R.  相似文献   

11.
A cobalt(salen) complex has been shown to catalyse the asymmetric Darzens condensation between α-haloamides and aldehydes, allowing both the relative and absolute stereochemistry of the epoxy-amide products to be controlled. Under optimal conditions, cis-epoxides can be obtained diastereoselectively with up to 50% enantiomeric excess, whilst by changing the leaving group and base, trans-epoxides can be produced diastereoselectively with up to 43% enantiomeric excess.  相似文献   

12.
《Tetrahedron: Asymmetry》1999,10(5):869-875
By the adoption of a regio- and stereoselective intramolecular radical cyclisation reaction onto a chiron derived from diacetone glucose, the crucial cis-fused bicyclo[3.3.0]octane system was made and utilized for the first synthesis of discosiolide 1, thereby establishing the absolute stereochemistry of the natural product.  相似文献   

13.
The C14-C24 fragment of symbiodinolide possessing the 17R/18R/21R absolute configuration, which was obtained as one of the degraded products of symbiodinolide, and its diastereomer possessing the 17R/18S/21R absolute stereochemistry were synthesized stereoselectively from cis-2-butene-1,4-diol, respectively. The detailed comparison of the synthetic products with the degraded product in the spectroscopic data confirmed unambiguously that the stereostructure of the C14-C24 fragment was 17R, 18R, and 21R.  相似文献   

14.
The structures of absolute configurations of the halogenated vinyl acetylenes which are natural products from the red alga Laurencia pinnatifica (Gmal. Lamour) are described. The structure of trans- pinnatifidenyne 2 was determined by spectral, chemical and X-ray diffraction analyses. The structure of cis-pinnatifidenyne 1 is based on spectral comparison and chemical interconversion with the trans-isomer 2. The structure of the acyclic trienyne 8 was secured as: (6R,7R)-3-cis, 9-cis,12-cis,6-acetoxy,7-chloropentadeca-3,9,12-trien-1-yne by synthesis from cis-pinnatifidenyne 1. The reactivity of these compounds to various conditions of catalytic hydrogenation has been examined in detail.  相似文献   

15.
《Tetrahedron》2004,60(5):1073-1078
New degraded and rearranged diterpenoids, 5-8, have been isolated from the Antarctic sponge Dendrilla membranosa. The structure and relative stereochemistry of these compounds were determined by spectroscopic data. The absolute stereochemistry of 5 was determined by spectroscopic data using a chiral reagent. Conformational studies allowed us to assign also the absolute stereochemistry of 6-8, as well as those previously isolated spongian-derived metabolites with known relative stereochemistries.  相似文献   

16.
The structure of bertyadionol, a member of a new class of diterpenes, has been elucidated by chemical and physical methods. The absolute configuration of the cyclopropane ring was determined by degradation of bertyadionol to (?)-cis-homocaronic acid dimethyl ester. Application of Nuclear Magnetic Double Resonance techniques, INDOR and NOE measurements, allowed the determination of the absolute stereochemistry of two of its derivatives.  相似文献   

17.
Six new compounds, named litsenolides A1, A2, B1, B2, C1 and C2, have been isolated from the roots of Litsea japonica (Japanese name “Hamabiward). Spectral and chemical evidence shows that these six compounds are three pairs of β-hydroxy-γ-methyl-αβ′-unsaturated-γ-lactones having a long carbon chain terminated with a methyl (C series), an allyl (A series) or a propargyl (B series) group. The two components of each pair differ only in the structure, cis or trans, at the double bond conjugated with the lactone group. The absolute stereochemistry of the compounds is also discussed.  相似文献   

18.
(+)-cis-4-Hydroxy-6-deoxyscytalone, a natural product bio-synthesized by Colletotrichum sp., has been prepared and its absolute configuration confirmed as 3R,4S, the key step being a kinetic racemic resolution of a cis-diol easily obtained from commercial 1,2,3,4-tetrahydronaphthalen-1,5-diol. Four lipases and different reaction conditions were tested in order to obtain the best yield and enantiomeric excess. Confirmation of absolute configuration was made by NMR using a single-derivatization low-temperature procedure and MPA as the auxiliary reagent.  相似文献   

19.
The novel nor-sesquiterpenoids, the davanafurans, have been isolated from the oil of Artemisia pallens, the principal component being the cis, threo-isomer ( 1a ). The absolute configuration of this isomer, and the relative stereochemistry of the other isomers, have been established by synthesis from linalool oxides of known configuration.  相似文献   

20.
In reactions of (2,3-anti)-3-amino-1,2-diols with diphosgene and phosgene and their conversion into 1,3-oxazolidin-2-ones, some differences in the stereochemistry of the reactions have been found with these two reagents. The reactions with phosgene afforded the expected cis-oxazolidinones, and in the reaction with diphosgene under the same reaction conditions, the trans-oxazolidinones were also obtained.  相似文献   

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