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1.
By the self-immolative asymmetric synthesis, optically pure key intermediate β-piperonyl-γ-lactone (R)-(+)- was found to be prepared in reasonable yield from the easily available chiral γ-lactone synthon () which had been also reported to give an antipode (S)-(-)-. The optically pure (R)-(+)- was shown to be converted successfully into several optically pure natural lignan lactones. 相似文献
2.
TiCl4 catalyzes the essentially quantitative coupling of chiral acetals with 1--butoxy-1--butyldimethylsilyloxyethene to generate β-alkoxycarboxylates in which the new asymmetric center is formed with excellent diastereoselection. β-hydroxycarboxylic acids of high ee result from removal of the chiral auxiliary. The procedure has been applied to the synthesis of R-(+)-α-lipoic acid 相似文献
3.
Keisuke Suzuki Eiji Katayama Katsuhiko Tomooka Takashi Matsumoto Gen-ichi Tsuchihashi 《Tetrahedron letters》1985,26(31):3707-3710
All four diastereomere of chiral alcohol with three contiguous chiral centers were stereoselectively prepared via diastereoselective addition of nucleophiles (crotyl metal or H-) to α-methyl-β,γ-unsaturated carbonyl compounds . 相似文献
4.
The readily-obtained carbohydrate α-enones , and are converted into the four diastereomeric 2,4-di-C-methyl glycopyranosides ,,, which are chiral synthons for the four multistriatins -. 相似文献
5.
(+)--(α-Bromocamphor-π-sulphonyl)-hydroxylamine, (1), a chiral amination reagent, converts prochiral sulphides into diastereomeric aminosulphonium α-bromocamphor-π-sulphonates This reaction forms the basis of a convenient synthesis of enantiomerically homogeneous ()-methyl--tolyl sulphoxide, a key compound in sulphur chemistry. 相似文献
6.
The major precursor to the maytansinoids containing 4 non-racemic chiral centers has been prepared in gram quantities, suitable for further synthesis. The route to (+)- was accomplished in 13 steps including several highly stereocontrolled reactions which precluded resolutions or separations. 相似文献
7.
(+)-Thalictrifoline () has been synthesized from an optically resolved (+)-8-oxo-13-carboxytetrahydroprotoberberine () whose absolute configuration was established by correlation with (+)-. This determines the absolute configurations of (+)-thalictrifoline () as 13R, 14R aria (+)-corydalic acid methyl ester () as 3R, 4R. 相似文献
8.
A new synthesis of (±), (+)- and (-)-lineatin (3,3,7-trimethyl-2, 9-dioxatricyclo [3.3.1.04,7] nonane, ) was achieved. The stereochemistry of (+)-lineatin was established as 1, 4, 5, 7 by an X-ray crystallographic analysis of an intermediate . 相似文献
9.
U. Berg R. Isaksson J. Sandström U. Sjöstrand A. Eiglsperger A. Mannschreck 《Tetrahedron letters》1982,23(41):4237-4240
(+)- and (?)- as well as (+)- and (?)- were partially separated by liquid chromatography on triacetylcellulose; racemizations resulted in the barriers (Table 2) to rotation via planarized transition states. 相似文献
10.
Felix H. Cano Concha Foces-Foces Manuel Bernabe Jesus Jimenez-Barbero Manuel Martin-Lomas Soledad Penades-Ullate 《Tetrahedron》1985,41(18):3875-3886
X-Ray and 1H N.M.R. studies on pyranoid rings 1,2--fused to dioxolane rings in acetylated -gluco- and --galactopyranose derivatives demonstrate that the configuration of the dioxolane ring influences the conformation of the pyranoid ring in the -gluco but not in the -galactopyranose series. The crystal structure of 3,4,6-tri--acetyl-1,2--(R)--(l-cyano-ethylidene)-α--glucopyranose () and 3,4,6-tri--acetyl-1,2--()-(1-cyano-ethylidene)-α--galactopyranose ()have been determined by X-ray analysis. Lattice parameters for are a=20.6021 (11), b=8.0438 (2), c=5.5541 (1) Å and β= 95.588 (3)° for a cell with P21 symmetry. These parameters for are a=20.3361 (7), b=10.0907 (2), c=18.9115 (5) Å, β =112.399 (2)°, C2, with two crystallographycally independent molecules. The conformation of the pyranoid ring in both compounds can be described as flattened 4C1 and that of the dioxolane ring as distorted E1. The importance of the torsion angles for describing problems of configuration is remarked and the use of relative configurational angles is stressed. The 1H N.M.R. spectra of and and 3,4,6-tri--acetyl-1,2-O-(S)- and (R)-ethylidene-α--glucopyranose ( and ), 3,4,6-tri-O-acetyl--1,2-O-(S)- and ()-ethylidene-α--galactopyranose ( and ), and 3,4,6-tri--acetyl-1,2--()-and ()-benzylidene-α--glucopyranose ( and ) have been analyzed by using iterative computer methods and N.O.E. measurements. The results indicate that the major solution conformation of the pyranoid ring of the derivatives in the -gluco series , and may be described as flattened 4C1 and that of and as 25. The major solution conformation of the pyranoid ring in all compounds in the -galacto series (,,,) may be described as flattened 41. 相似文献
11.
The α-anions of 2-substituted 1,3-dioxolan-4-ones derived from chiral mandelic and lactic acid (, ; ; , ) were alkylated with high stereoselectivity. The products formed were hydrolysed to α-hydroxy acids with 65–85% e.e. ((S)(+)-,,, (R)(–)-). 相似文献
12.
Thomas W. Bell 《Tetrahedron letters》1980,21(36):3443-3446
Hydroboration-oxidation of the bi-1-cyclohexen-1-yls 1 and 8b gave single 1,4-diols, 2 and 10b, respectively, whereas the chiral bi-1-cyclohexen-1-yl 8a, synthesized from (?)--3,5-dimethylcyclohexanone, led to a mixture of two 1,4-diols (9a and 10a). 相似文献
13.
(±)-7-Deoxy-4-demethoxydaunomycinone(±)-) was cleanly resolved by forming a mixture of the diastereomeric acetals ((?)- and (+)- or (+)- and (?)- with the title -diol((+)- or (?)-) to give optically pure (R)(?)-. The method for racemizing the undesired enantiomer((S)(+)-) was also explored. Optically pure (+)-4-demethoxydauno-mycinone ((+)-) was elaborated from (R)(-)- according to the reported reaction scheme. 相似文献
14.
Simon J. Edge W.David Ollis Julia Stephanidou Stephanatou J.Eraser Stoddart David J. Williams Kwamena A. Woode 《Tetrahedron letters》1981,22(23):2229-2232
The tri-3-methyltrianthranilide derivatives ()–() have been synthesised. Dynamic 1H n.m.r. spectroscopy indicates that the ,′,″-trimethyl derivative () exists in solution as slowly ring inverting ( ? *) enantiomeric helical conformations. X-Ray crystallography shows that the ,′-dimethyl-″-benzyl derivative () undergoes spontaneous resolution when it crystallises as a 1:1 adduct from toluene. The host molecules adopt a helical conformation (Figure 1) within a lattice structure that contains chiral channels (Figure 2) occupied by guest solvent molecules. 相似文献
15.
Wolfgang Oppolzer Mark Kurth Daniel Reichlin Frank Moffatt 《Tetrahedron letters》1981,22(27):2545-2548
The chiral induction in the Diels-Alder addition → , assessed reliably by 19F-NMR-spectroscopy of the endo-esters , varied between 47 - 93% in favor of the 2-(R)-adducts depending on the auxiliary chiral group and the Lewis-acid catalyst. 相似文献
16.
The title reactions performed with (S)-α-amino acids or their derivatives as chiral sources were found to regioselectively give enantiomeric pairs of optically active 4-acetyl-3, 4-dimethyl-2-cyclohexenone (R)(+)- and (S)(?)-), 16–25% e.e., and those of optically active 6-acetyl-3,6-dimethyl-2-cyclohexenone((R)(+)- and (S)(?)-, 54–59% e.e., from the open chain triketone(). 相似文献
17.
Wolfgang Oppolzer Christian Chapuis Guo Mao Dao Daniel Reichlin Thierry Godel 《Tetrahedron letters》1982,23(46):4781-4784
Starting from (R)-(+)- and from (S)-(?)-camphor the chiral alcohols , and have been prepared; their acrylates II underwent TiCl2(OR)2-promoted Diels-Alder additions to cyclopentadiene giving efficiently in a predictable manner either the (2R)- or the (2S)-adducts III with up to virtually quantitative asymmetric induction. 相似文献
18.
Reaction of ,,,-[9]annulene anion () with electrophiles (-) leads to substituted ,,,-1,3,5,7-cyclononatetraenes (-) which are precursors for the preparation of 10- and 10,10′-donor-substituted nonafulvenes (e.g. ). The influence of solvent and temperature on the 1H-nmr spectra of the nonafulvenes - has been investigated. 相似文献
19.
Thomas J. Simpson 《Tetrahedron letters》1981,22(38):3785-3788
Incorporations of [1-13C]?, [2-13C]?, [1,2-13C2]-acetates and [13C]-methionine into anditomin, a metabolite of , indicate its formation by a mixed polyketide-terpenoid biosynthetic pathway similar to that elucidated for andibenin; observations are made on the possible biosynthetic relationship of the metabolites with austin and terretonin, mycotoxins recently isolated from and respectively. 相似文献
20.
- and -2-Methylamino and 2-benzylamino-3-hydroxymethylbicyclo [2.2.1]heptanes and the corresponding bicycio [2.2.1] heptenes ( -, -) were synthesized from β-amino acid esters containing the norbornane or norbornene skeleton (-). The aminoalcohols were converted to 5,8- methano -3,1-benzoxazines by reaction with formaldehyde. As established by 1H and 13C NMR spectroscopy, the predominant conformation is () for the , and () for the derivatives. 相似文献