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1.
Robert Glaser Itay Adin David Ovadia Ernestine Mendler Marc Drouin 《Structural chemistry》1995,6(3):145-156
Single-crystal X-ray diffraction analysis was used to determine the structure of a racemic diastereomer of the agricultural fungicide propiconazole [1-(2-(2,4-dichlorophenyl)-4-n-propyl-1,3-dioxolane-2-yl-methyl)-1-H-1,2,4-triazole] and of two by-products (a symmetrical 1,3,4-triazole racemic-constitutional isomer and a propiconazole ditriazole analogue). All three crystalline racemic-diastereomers had (2R,4S)/(2S,4R)-stereochemistry in which then-propyl group was observed in atrans-to-phenyl disposition. Propiconazole (2R,4S)/(2S,4R)-diastereomer gives crystals belonging to the monoclinic space group P21,/a, and, at 293 K,a=8.1192(3),b=18.9769(6),c=10.7137(4) å,Β=99.765(3)?,V=1626.8(1) å3, Z=4,R(F)=0.060, andR w(F)=0.058. The constitutional isomer by-product (2R,4S)/(2S,4R)-1-(2-(2,4-dichlorophenyl)-4-n-pro-pyl-1,3-dioxolane-2-yl-methyl)-1-H-1,3,4-triazole gives crystals belonging to the monoclinic space group P21/n, and, at 293 K,a=11.1763(6),b=10.7716(4),c=14.5804(8) å,Β=107.445(4)?,V=1674.6(1) å3, Z=4,R(F)=0.043, andR w(F)=0.043. The ditriazole byproduct (2R,4S)/(2S,4R)-1-(2-(2-chloro-4-(1,2,4-triazole-1-yl)phenyl)-4-n-propyl-1,3-dioxolane-2-yl-methyl)-1-H-1,2,4-triazole gives crystals belonging to the triclinic space groupP¯ 1, and, at 193 K,a=5.3329(8),b=8.3738(7),c=20.240(2) å, α=84.213(6)?,Β=87.20(1)?,γ=86.23(1)?,V=896.5(2) å3, Z=2,R(F)=0.046, andR w(F)=0.051. The presence of both propiconazole (2R.4S)- and (2S,4R)-enantiomers enables the formation of a crystalline racemic modification, while the diastereomeric propiconazole (2R,4R)- and (2S,4S)-enantiomers are viscous oils. In the absence of its enantiomorphic partner, the propiconazole (2R,4S)- or (2S,4R)-enantiomers remain as viscous oils rather than form chiral crystals. 相似文献
2.
Amalia M. Estévez Raquel G. Soengas José M. Otero Juan C. Estévez Robert J. Nash Ramón J. Estévez 《Tetrahedron: Asymmetry》2010,21(1):21-26
A divergent synthesis of the two novel polyhydroxylated azepanes (2R,3R,4R,5R,6R)-2-(hydroxymethyl)azepane-3,4,5,6-tetraol and (2R,3R,4R,5R,6S)-2-(hydroxymethyl)azepane-3,4,5,6-tetraol from d-mannose is described. The method involves a Henry reaction between dimethyl-tert-butylsilyl 2,3-O-isopropylidene-α-d-lyxo-pentodialdo-1,4-furanoside and 2-nitroethanol followed by a reductive ring closure of the resulting epimeric nitro aldols. Glycosidase inhibition tests showed that (2R,3R,4R,5R,6S)-2-(hydroxymethyl)azepane-3,4,5,6-tetraol exhibits a weak but selective inhibition against α-l-fucosides. 相似文献
3.
《Tetrahedron: Asymmetry》2007,18(4):513-519
Total synthesis of (4R,5S,6E,14S)- and (4R,5S,6E,14R)-cystothiazoles F 3 was achieved from the chiral bithiazole-type primary alcohols [(S)- and (R)-4-ethoxycarbonyl-2′-(1-hydroxymethylethyl)-2,4′-bithiazoles 8], which were obtained based on the enzymatic resolution of racemic alcohol 8 and its acetate 9. From a direct comparison by means of chiral HPLC between natural cystothiazole F 3 and synthetic compounds [(4R,5S,6E,14S)- and (4R,5S,6E,14R)-cystothiazoles 3], natural cystothiazole F 3 was found to be a 33:67 diastereomeric mixture [(4R,5S,6E,14S)-3:(4R,5S,6E,14R)-3 = 33:67]. 相似文献
4.
《Tetrahedron: Asymmetry》1998,9(13):2329-2332
The synthesis of enantiomerically pure (2S,3R,4R)-ethoxycarbonylcyclopropyl phosphonoglycine is described, the key-step involving 1,4-addition of a chiral enolate to ethyl 4-bromo-crotonate. 相似文献
5.
《Tetrahedron: Asymmetry》2006,17(20):2876-2883
An efficient and a convenient enantioselective synthesis of (3R,4S)-3-methoxy-4-methylaminopyrrolidine has been carried out by a lipase-mediated resolution protocol. This method describes the preparation of (±)-1-Cbz-cis-3-azido-4-hydroxypyrrolidine starting from commercially available diallylamine followed by ring-closing metathesis (RCM) via SN2 displacement reactions. Pseudomonas cepacia lipase immobilized on diatomaceous earth (Amano PS-D) provides (3R,4S)-11 and (3S,4R)-12 in an excellent enantiomeric excess. 相似文献
6.
《Tetrahedron: Asymmetry》2006,17(14):2133-2142
(S)-Perillyl alcohol was converted to (R)-cryptone (91.5–93% ee) in six steps, which was then treated with methyllithium to give (1S,4R)-4-isopropyl-1-methyl-2-cyclohexen-1-ol, the aggregation pheromone of the ambrosia beetle Platypus quercivorus. The racemic pheromone was also prepared by methylation of (±)-cryptone. Both (1R,4R)- and (1S,4S)-isomers (98% ee) of the pheromone were synthesized from the enantiomers of dihydrolimonene oxide. 相似文献
7.
Fernando Fernández Amalia M. Estévez Juan C. Estévez Ramón J. Estévez 《Tetrahedron: Asymmetry》2009,20(6-8):892-896
The first total synthesis of a new enantiopure polyhydroxylated cyclopentyl β-amino acid [methyl (1S,2R,3S,4R,5S)-2-benzyloxy-5-benzyloxycarbonylamino-3-hydroxy-4-methoxycyclopentanecarboxylate] was achieved according to our recent novel strategy for the transformation of nitrohexofuranoses into cyclopentylamines. This approach is based on an intramolecular cyclization leading to 2-oxabicyclo[2.2.1]heptane derivatives. Epimerization of this amino acid derivative to methyl (1S,2R,3R,4R,5S)-2-benzyloxy-5-benzyloxycarbonylamino-3-hydroxy-4-methoxycyclopentanecarboxylate constitutes the first example of the preparation of one of the members of this family of amino acids with a stereochemistry that is not compatible with the above key cyclization step. 相似文献
8.
《Tetrahedron: Asymmetry》2007,18(13):1585-1588
A novel four step synthesis of enantiomerically pure (2S,3R,4R,5S)-trihydroxypipecolic acid, starting from readily available materials, that is, condensation products of (R)-(−)-phenylglycinol with a mesotrihydroxylated glutaraldehyde, is described. The scope and limitations of the reaction have also been investigated. 相似文献
9.
Patrizia Ferraboschi Maria De Mieri Paride Grisenti Matthias Lotz Ulrike Nettekoven 《Tetrahedron: Asymmetry》2011,22(16-17):1626-1631
The synthetic antithrombotic argatroban is a dipeptide between the nonproteogenic (2R,4R)-4-methyl-2-piperidine carboxylic acid and l-arginine, in turn bonded to a methyltetrahydroquinoline sulfonyl group. An extensive screening of transition metal-based complexes with different ligands was performed in order to identify the best catalyst for the diastereoselective hydrogenation of a suitable 4,5-dehydropiperidine precursor aimed toward a synthesis of the (2R,4R)-4-methyl piperidine moiety. 相似文献
10.
《Tetrahedron》2017,73(1):39-45
Synthesis of a unique fatty acyl unit to build the N-terminus of callipeltin A and homophymine B is described. Our approach to access (2R, 3R, 4R)-3-hydroxy-2,4,6-trimethylheptanoic acid uses enzymatic hydrolysis for the desymmetrization of achiral acetate, followed by diastereoselective Roush crotylboration and Wittig olefination for the backbone construction. 相似文献
11.
N. A. Ivanova Z. R. Valiullina O. V. Shitikova M. S. Miftakhov 《Russian Journal of Organic Chemistry》2006,42(11):1701-1705
Methyl (1S,2S,3R,4R)-2,3-isopropylidenedioxy-5-iodomethyl-2-tetrahydrofurylacetate prepared in two stages from D-ribose acetonide underwent a series of uncommon transformations under the treatment with bases providing the following different products depending on the base applied: methyl 3-(5-acetyl-2,2-dimethyl-1,3-dioxol-4-yl)propionate (DBU), methyl 2,3-isopropylidenedioxy-7-oxabicyclo[2.2.1]heptane-6-carboxylate (t-BuOK), methyl {(5R)-2,2-dimethyl-5-[(2R)-oxiranyl]-1,3-dioxolan-4-ylidene}propionate and methyl-(E)-3-{(4S,5R)-2,2-dimethyl-5-[(1R)-(2-oxiranyl)]-1,3-dioxolan-4-yl}-2-propenoate (t-BuOK and LDA). 相似文献
12.
G. Yu. Ishmuratov A. V. Bannova E. R. Latypova R. R. Muslukhov A. A. Smol′nikov R. F. Talipov 《Chemistry of Natural Compounds》2012,48(5):789-790
A modified stereospecific synthesis of potentially biologically and pharmacologically active methyl (1R,2R,3E,5R)-3-(hydroxyimino)-5-methyl-2-(1-methylethyl)cyclohexanecarboxylate from (R)-4-menthen-3-one was developed using sequential 1,4-conjugate addition of Norman reagent catalyzed by CuI?CBF3?Et2O?CCuCl2 and ozonolysis?Creduction of the intermediate (R,R,R)-vinylmenthone by hydroxylamine hydrochloridein MeOH. 相似文献
13.
《Tetrahedron: Asymmetry》2000,11(7):1585-1592
lyxo-C18-Phytosphingosine can be synthesized by the cis-dihydroxylation of an (E)-allylic trichloroacetamide obtained by an Overman rearrangement. A double stereodifferentiation using AD-mix-β and an enantiomerically enriched (S)-allylic trichloroacetamide allowed the first synthesis of lyxo-(2R,3R,4R)-C18-phytosphingosine with high diastereoselectivity (de=94%) and excellent enantioselectivity (ee=93%). This sphingosine was fully characterized by the physical and spectral data of the corresponding tetraacetate. 相似文献
14.
(2R,3R,4S)-4-Amino-7-guanidino-2,3-dihydroxyheptanoic acid (AGDHE), a common constituent of biologically active marine peptides, callipeltin A (1) and neamphamide A, was synthesized as its orthogonally protected derivative from l-glutamic acid in 15 steps. Guanidination by the Mitsunobu condition and osmium-catalyzed dihydroxylation of the corresponding Z-olefin were employed as the key steps. 相似文献
15.
G. Yu. Ishmuratov V. S. Tukhvatshin R. R. Muslukhov A. S. Erastov A. V. Allagulova A. V. Bannova G. A. Tolstikov 《Russian Journal of Organic Chemistry》2014,50(1):133-136
Ozonolysis of (1R,3R)-p-menth-4-en-3-ol in methylene chloride or methanol in the presence of pyridine afforded a mixture of equimolar amounts of epimeric 1-[(2R,4S,6S)- and 1-[(2S,4S,6S)-6-hydroxy-4-methyltetrahydro-2H-pyran-2-yl]-2-methylpropan-1-ones. A probable reaction mechanism is discussed. 相似文献
16.
《Tetrahedron: Asymmetry》1998,9(8):1395-1407
Two different methods for preparing the thiazole analogue 3 of the biologically active compound (1R,2S,3R)-2-acetyl-4(5)-(1,2,3,4- tetrahydroxybutyl)imidazole 1 are reported. 相似文献
17.
Stephen G. Davies Rosemary Huckvale Thomas J.A. Lorkin Paul M. Roberts James E. Thomson 《Tetrahedron: Asymmetry》2011,22(14-15):1591-1593
A concise asymmetric synthesis of the gastroprokinetic agent (+)-(3S,4R)-cisapride {(+)-(3S,4R)-N(1)-[3′-(4″-fluorophenoxy)propyl]-3-methoxy-4-(2″′-methoxy-4″′-amino-5″′-chlorobenzamido)piperidine} from commercially available starting materials has been developed. The key step of this synthesis employs the diastereoselective conjugate addition of lithium (R)-N-benzyl-N-(α-methylbenzyl)amide to tert-butyl 5-[N-3′-(4″-fluorophenoxy)propyl-N-allylamino]pent-2-enoate and in situ enolate oxidation with (?)-camphorsulfonyloxaziridine to set the (3S,4R)-configuration found within the piperidine ring of the product. This synthesis proceeds in 9 steps from commercially available 1-(4′-fluorophenoxy)-3-bromopropane with an overall yield of 19%. 相似文献
18.
The total and semi syntheses of (2R,3R)-epigallocatechin-3-O-(4-hydroxybenzoate), a novel catechin from Cistus salvifolius, were accomplished. The proteasome inhibition and cytotoxic activities of the synthetic compound and its acetyl derivative were studied and compared with (2R,3R)-epigallocatechin-3-gallate (EGCG), the active component from green tea. 相似文献
19.
《Tetrahedron: Asymmetry》2006,17(1):79-91
Reductions of (1R,3R,4R)-3-([1,2,4]triazolo[4,3-x]azin-3-yl)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ones and their lactone analogues, prepared from (1R)-(+)-camphor, were studied. Catalytic hydrogenation selectively led to partial saturation of the [1,2,4]triazolo[4,3-x]azine residue, while in reactions with borane–methylsulfide coordination of borane to the 1-position of [1,2,4]triazolo[4,3-x]azine system took place. On the other hand, activation of the carbonyl group in (1R,3R,4R)-3-([1,2,4]triazolo[4,3-x]azin-3-yl)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ones with boron trifluoride etherate followed by reaction with borane–methylsulfide furnished the corresponding isoborneols, stereoselectively. The structures of all representative compounds were confirmed by X-ray diffraction. 相似文献
20.
N. K. Selezneva F. A. Gimalova R. F. Valeev M. S. Miftakhov 《Russian Journal of Organic Chemistry》2011,47(2):173-179
A simple and convenient one-pot synthesis of (1R,4S,6R)-4-isopropenyl-1,3,3-trimethyl-7-oxabicyclo[4.1.0]heptan-2-one was developed consisting in a thermodynamic methylation of carvone (NaH, MeI, THF, 20°C) followed by the epoxidation with alkalinized hydrogen peroxide. The reduction of the obtained epoxyketone with sodium borohydride proceeded stereoselectively to give a β-alcohol. The attempts to convert its isopropenyl fragment into an acetate group by a rearrangement of products or intermediates of the oxidative fragmentation resulted only in obtaining intermediate acyl derivatives. 相似文献