Quaternary ammoniums and a cationic sodium complex as supramolecular catalysts in ring-opening of epoxides by amines

Supramolecular ionic organocatalysts and a metal-based catalyst were investigated in the ring-opening of epoxides by amines, without any artifice to enhance conversion (i.e., solvophobic effect, extended reaction time, heating, excess of amine, high catalyst loading). Different β-amino-alcohols were obtained in satisfying conversion (50–80%) in 24 h, under mild conditions.     

Ring opening of disubstituted epoxides linked to a secondary oxygen group with an organocopper reagent

Coupling reactions of epoxide linked to a secondary oxygen group with Gilman reagents were examined. The regiochemical direction depended on whether there is TMS or MOM as a protective group of the secondary alcohol. anti-Epoxy alcohol 6 tended to react with Me₂CuLi at the C4 position to generate 1,2-diol 22 as a major component. Epoxide 7 linked to a trimethylsilyloxy group displayed selective formation of 1,3-diol 18. On the other hand, the reactions of syn-epoxy alcohol 12 and the corresponding TMS ether 13 resulted in the selective formation of 1,2-diol 25.     

Naturally occurring scaffolds for compound library design: convenient access to bis-aryl 1-azaadamantanes carrying a vicinal amino alcohol motif

The vast majority of scaffolds found in natural products are absent from the currently available compound collections for biological screening. At the same time, scaffolds derived from natural products may have a distinct advantage over non-natural cores in terms of providing compounds endowed with biological activities and should be used extensively in screening library design. We have developed a synthetic approach to merging a naturally occurring 1-azaadamantane core with a vicinal amino alcohol moiety that is also common in natural product chemical space. The synthesis features diastereoselective epoxidation of racemic chiral 2,6-diaryl-4-methylene 1-azaadamantanes with subsequent S_N2-type epoxide opening in aqueous isopropanol.     

Asymmetric Ring-Opening of Cyclohexene Oxide with Mercaptan (Thiophenols) Catalyzed by Chiral Schiff Base/Ti(OPr- i ) 4 or (−)-(S)-Binaphthol/Ti(OPr- i ) 4

New chiral Schiff base ligands 1-4 were synthesized starting from (+)-camphor and (+)-1-(4-nitrophenyl)-2-amino-1,3-propanediol, and their application in asymmetric ring-opening of cyclohexene oxide using mercaptan (thiophenols) as nucleophiles was investigated. The aymmetric ring-opening of cylohexene oxide catalyzed respectively by chiral Schiff bases 1-4 /Ti(OPr- i ) 4 and ( m )-(S)-1,1'-binaphthalene-2,2'-diol 5 /Ti(OPr- i ) 4 complex afforded the corresponding chiral g -hydroxysulfides 6-10 in lower to good yield with lower to moderate ee values. Moreover, the using of ( m )-(S)-1,1'-binaphthalene-2,2'-diol as ligand led to better chiral induction effect.     

A Green Protocol for the Easy Synthesis of Thiiranes from Epoxides Using Thiourea/Silica Gel in the Absence of Solvent

The use of thiourea/silica gel provides a green protocol for the easy and high-yielding preparation of thiiranes from different classes of epoxides in the absence of solvent at room temperature. The high stereospecific conversion of (R)(+)-styrene oxide to (S)(+)-styrene sulfide is also reported using this reagent system.     

Aromatic amine mediated ring opening of epoxides: A reaction catalyzed by biogenic iron oxide nanoparticles

An efficient green method was used for the synthesis of polyphenol capped iron oxide nanoparticles (ION) from an agro waste, peanut skin. The polyphenol capped ION was characterized by Fourier transformed infra-red (FTIR), Powder XRD and X-ray photoelectron spectroscopic (XPS) analysis. To evaluate the catalytic activities of ION, ring opening of epoxides by aromatic amines has been performed and the catalyst showed good activity with yields up to 90% of the major products using only 20 ​mg of the catalyst under solvent free neat condition at room temperature (28 ​°C) after 5 ​h. These nanoparticles can be reused for three times without significant loss in their activities.     

稀土化合物催化内酯开环聚合(Ⅲ)──氯化钕-环氧化合物体系催化ε

Bulk polymerization of ε-caprolactone(CL) with neodymium chloride-epoxide sys tem has been studied. It was found that the addition of epoxide can greatly increase the catalytic activity of neodymium chloride. The catalytic activity sequence of NdCl₃ combined with epoxide is: NdCl₃-ethylene oxide > NdCl₃-proplene oxide > NdCl₃-epichlorohydrin≈NdCl₃-allyl glycidyl ether. The catalytic activity of NdCl₃-proplene oxide system increases,but molecular weight of resulting polycaprolactone(PCL) decreases at higher proplene oxide/ neodymium chloride molar ratio.The molecular weight of PCL can be controlled by catalyst concentration. Higher polymerization temperature can greatly increase the catalytic efficien cy. At 30℃, PCLwith molecular weight as high as 28. 9×10⁴can be prepared easily with an activity of 44×10⁴g PCLper molar neodymium, and at 60℃, the molecular weight of PCLand catalytic efficiency increased to 42×10⁴and 10⁶g PCL/mole Nd respectively.     

Isomers of neplanocin A and 2′-deoxyneplanocin A possessing a C-1′/C-6′ double bond

Missing among the unsaturated carbocyclic nucleosides is the 1′,6′-double bond isomer of neplanocin A. A practical synthesis of this compound and its 2′-deoxy derivative is reported from readily accessible cyclopentenols.     

Facile epoxidation of alpha,beta-unsaturated ketones with cyclohexylidenebishydroperoxide

Cyclohexylidenebishydroperoxide was successfully used as the oxygen source for the oxidation of α,β-unsaturated ketones for the first time. The corresponding epoxides were obtained in excellent yields under the Weitz-Scheffer reaction conditions.     

A concise synthesis of protected (2S,4R)-4-hydroxyornithine

A short synthesis of the nonproteinogenic amino acid, (2S,4R)-4-hydroxyornithine is described. Starting from racemic benzyl glycidol, the scaffold of the target compound was constructed in high enantio- and diastereoselectivity using Jacobsen’s hydrolytic kinetic resolution (HKR) and regioselective opening of an epoxide as key steps.