Stereoselective epoxidation of 4-fluoro-4-nitrocyclohexenes

Novel fluorinated α-epoxycyclohexanes were synthesized in up to 96% yields by epoxidation of the Diels–Alder adducts of β-fluoro-β-nitrostyrenes and 2,3-dimethylbuta-1,3-diene. The epoxidation with m-chloroperoxybenzoic acid and subsequent hydrolysis into diols were found to proceed in a highly stereoselective manner.     

Stereoselective stilbene epoxidation over supported gold-based catalysts

The gold reference catalyst Au/TiO(2) exhibits high activity in the stereoselective epoxidation of trans-stilbene in methylcyclohexane in the presence of 5 mol% TBHP, by taking part in a chain reaction involving the activation of molecular oxygen by a radical produced from methylcyclohexane.     

Stereoselective epoxidation of 4-deoxypentenosides: a polarized-pi model

The high facioselectivity in the epoxidation of 4-deoxypentenosides (4-DPs) by dimethyldioxirane (DMDO) correlates with a stereoelectronic bias in the 4-DPs' ground-state conformations, as elucidated by polarized-pi frontier molecular orbital (PPFMO) analysis.     

Stereoselective peracid epoxidation of allylic and δ-hydroxyallylic diphenylphosphine oxides

The title compounds were epoxidised by $\text{m}$-chloroperbenzoic acid with high stereoselectivity induced by the Ph₂PO or hydroxyl groups.     

Stereoselective intramolecular [4 + 3] cycloadditions of nitrogen-stabilized chiral oxyallyl cations via epoxidation of N-tethered allenamides

The first intramolecular [4 + 3] cycloaddition reaction using nitrogen-stabilized chiral oxyallyl cations that are tethered to furan or diene through the nitrogen atom is described here. Formation of these nitrogen-stabilized chiral oxyallyl cations is achieved by a chemoselective epoxidation of chiral allenamides via syringe pump addition of dimethyl dioxirane. The ensuing cycloaddition can be carried out with a range of different lengths for the tether, and high diastereoselectivities can be obtained when using chiral allenamides with shorter tethers.     

Stereoselective epoxidation of 2-arylidene-1-indanones and 2-arylidene-1-benzosuberones

Summary Oxidation of the (E) and (Z) isomers of 2-arylidene-1-indanones (1) and 2-arylidene-1-benzosuberones (4) by alkaline hydrogen peroxide (methodi) afforded the spiroepoxidestrans-2a–g andtrans-5a–g from both isomers as sole products in high yields. On the other hand, dimethyldioxirane epoxidation(methodii) of the (E) isomers1a–g and4a–g gave the correspondingtrans spiroepoxides in good yields, whereas the (Z) isomers1a,c,e and4a,c,e led to thecis spiroepoxides in moderate yields. Dimethyldioxirane oxidation (methodii) of (Z)-1c and (Z)-4c,e gave diones3c and6c,e as by-products as well. Epoxidation of (Z)-1a,c,e and (Z)-4a,c,e bym-chloroperoxybenzoic acid (methodiii) resulted inca. 6:1 mixtures ofcis-2a,c,e andtrans-2a,c,e orcis-5a,c,e andtrans-5a,c,e spiroepoxides.Dedicated to Prof.W. Fleischhacker on the occasion of his 65^th birthday     

Stereoselective epoxidation of 5(10),9(11)-estradienes

3,3-(2,2-Dimethyltrimethylene-1,3-dioxy)-5(10),9(11)-estradien- 17-one is converted to its 5α,10α-epoxide by iron phthalocyanine/iodosylbenzene in a highly stereoselective manner.     

Stereoselective epoxidation of acyclic allylic alcohols. A correction of our previous work.

A reinvestigation of the stereoselectivities for the epoxidation of acyclic allylic alcohols with MCPBA, and with $\text{tert}$-butyl hydroperoxide catalyzed by V⁺⁵ and Mo⁺⁶ revealed a number of errors in our original work¹ which are rectified. Optimum O-C-C=C dihedral angles are proposed.     

Stereoselective synthesis of 2,3-difunctionalised thioesters using nucleophilic epoxidation of 1-arylthio-1-nitroalkenes

Stereoselective nucleophilic epoxidation of protected 3-amino and 3-hydroxy-substituted 1-arylthio-1-nitroalkenes, followed by intramolecular capture involving the amino and hydroxyl protecting groups, has led to the formation of isomeric oxazolidinones 5 and 7, and a cyclic carbonate 11. Together with the oxazolidinone precursor anti-alpha-bromo thioester 15a, the absolute and relative stereochemistry of these compounds has been determined by X-ray crystallography.     

Stereoselective synthesis of 3-heteroaromatic-substituted alanines

An asymmetric synthesis of (R)-3-heterocyclic-substituted alanines starting from (2S)-(+)-2,5-dihydro-3,6-dimethoxy-2-isopropylpyrazine (Schöllkopf reagent) and heteroaromatic halogenomethyl derivatives via hydrolysis of intermediate adducts is reported. The diastereocontrolled addition gives mainly compounds with the (2S,5R) configuration whose formation is explained on the basis of the accepted model for the alkylation reaction of the Schöllkopf reagent, and structure confirmed by spectroscopic data.     

Stereoselective synthesis of erythro-3-fluorophenylalanine

Reductive amination of 3-fluorophenylpyruvic acid was found to give erythro-3-fluorophenylalanine with high selectivity.     

Stereoselective synthesis of tetrahydrofuran-3-carbaldehyde

Trans-tetrahydrofuran-3-carbaldehydes are prepared by ruthenium-catalyzed isomerization of 4,7-dihydro-1,3-dioxepines and subsequent Lewis acid-catalyzed 1,3-alkyl migration.     

Enantioselective synthesis of 3-demethoxyaranciamycinone via asymmetric epoxidation

The tetracyclic olefin 1 was enantioselectively epoxidized using a molybdenum(VI)- oxodiperoxo complex containing a chiral lactamide. Conversion to the glycosides 8 and 9 showed the epoxide 2 to be the predominant (3 : 1) enantiomer.     

Stereoselective Synthesis of 2-Ethylidene-3-aminonitriles

2-(l-acetoxyethyl) acrylonitrile 1 can be stereoselectively converted into 2-ethylidene -3-aminonitriles 4 in good yields in the presence of primary or secondary arnines in THF at room temperature.     

Stereoselective iodolactonization of acyclic unsaturated 3-hydroxyacids

A stereoselective method for preparing 3-hydroxy-4-alkyl-γ-lactones is reported. iodolactonization of 3-hydroxy-4-alkenoic acids produces predominantly the thermodynamically less stable 3,4-cis products, which undergo methanolysis to $\text{threo}$-epoxyalcohols.     

Stereoselective epoxidation of alkenylidene acetals derived from carbohydrates with d-allo,d-altro,d-galacto,d-gluco and d-xylo configurations

The synthesis of 2,3-epoxypropylidene acetals of sugar derivatives from N-acetyl-2-amino-2-deoxy-d-allopyranose, d-altropyranose, d-galactopyranose, N-acetyl-d-glucosamine, d-glucofuranose and d-xylofuranose is described. The epoxidation with m-CPBA of the corresponding alkenylidene derivatives took place with different stereoselectivities depending upon the sugar configuration, the protecting group of the hydroxyl groups of the sugar, and the substitution of the unsaturated system. The analysis of the ring-opening reaction of these oxiranes by hydrogenolysis enabled the assignation of their configuration at the new stereogenic centres.     

新型3,3′-吡咯双螺环氧化吲哚类化合物的有机催化不对称合成

以3-异硫氰氧化吲哚(1)与3-烯氧化吲哚(2),经济易得的有机奎宁作为有机催化剂,在二氯甲烷溶剂中发生Michael加成环化反应,合成了12个未见文献报道的3,3′-吡咯双螺环氧化吲哚类化合物3a^3l,产率81%~92%,ee值86%~>99%,dr值7/1~>20/1,其结构经1H NMR,13C NMR和HR-MS(ESI-TOF)表征。通过培养3c(CCDC:1961579)和3j(CCDC:1961580)单晶,确定其绝对构型为(2′R,3′S,4′R)。