Nuclephilic ring opening of epoxides promoted by multi-site phase-transfer catalyst:An efficient and eco-friendly route to synthesis of b-hydroxy-thiocyanate

A highly effective and mild protocol for ring opening of epoxides with NH ₄ SCN in the presence of catalytic amount of a multisite phase-transfer catalyst, α,α',α -N-hexakis(triethylammoniummethylene chloride)-melamine, is developed. A variety of b-hydroxy thiocyanates as important intermediates in agricultural and pharmaceutical chemistry were obtained in high yields with excellent regioselectivity and in short reaction times.     

N-Methylative aziridine ring opening and asymmetric synthesis of MeBmt

Asymmetric synthesis of MeBmt, an unusual amino acid constituent of cyclosporine A, was achieved from aziridine-(2R)-carboxaldehyde through the highly stereoselective addition of (E)-crotylboronate and the subsequent N-methylative aziridine ring opening as key steps.     

A rare pyridine to pyrrole conversion leading to a side product in epoxide ring opening

A minor side product in a manufacturing batch of the intermediate 4 was observed and separated. The minor side product 5 was purified by preparative HPLC and its structure was determined by the analysis of comprehensive NMR and MS data. The structure of 5 reveals that its mechanism of formation includes a rare conversion of a pyridine moiety to a pyrrole.     

Anionic ring opening of norbornenes fused to heterocycles

The 2-hydroxy and 2-oxo derivatives of 1,2,3,4-tetrahydro-1,4-methanophenazine were prepared and found to evolve in basic media through the opening of their bicyclo[2.2.1]heptene moiety, affording 2,3-dihydro-1H-cyclopenta[b]quinoxaline derivatives with two-carbon 1-substituents that depend on the starting compound. In the case of 2-hydroxy starting compounds, ring-opening occurs regardless of the orientation of the hydroxyl group, and in methanolic solution is spontaneous, though slow, even in the absence of added base (at least in the case of the endo derivative). It is presumably favoured by the steric strain of the heteroaryl-fused bicyclo[2.2.1]heptene moiety, and is hypothesized to involve the base-promoted formation of anionic intermediates that are stabilized by the π-deficient nature of the quinoxaline system.     

Palladacycle as highly efficient catalyst for ring opening of oxabicyclic alkenes with organozinc halides

Ring opening reaction of oxabicylic alkenes 4 with in situ prepared organozinc halides 5 was catalyzed by palladacycle 3 with high efficiency. Good yields of the corresponding 1,2-dihydronaphth-1-ols (6) were provided when as low as 0.05 mol% of palladacycle 3 was used. ³¹P NMR study showed that the skeleton of 3 remained intact in the reaction, which implied that palladacycle 3 did not serve as a catalyst precursor but a catalyst in the reaction.     

The high-temperature alicyclic ring contraction of 1,1-dichloroperfluorotetralin and the alicyclic ring opening of 1,1-dichloroperfluorobenzocyclobutene

The pyrolysis of 1,1-dichloroperfluorotetralin (4) in a stream of argon gives a mixture contained perfluoro-1-methyleneindan (1), perfluoro-3-methylindene (6), 1,1-dichloroperfluoroindan (2) and perfluoroindene (7), while copyrolysis of tetralin 4 with CHClF₂ gives a mixture of compounds 1, 6 in the absence of compounds 2 and 7. 1-Chloro-2-(1-chloro-2,2-difluorovinyl)-3,4,5,6-tetrafluorobenzene (12) is formed in the pyrolysis of 1,1-dichloroperfluorobenzocyclobutene (5) in a stream of argon as well as in a stream of CHClF₂.     

Task specific ionic liquid as solvent,catalyst and reagent for regioselective ring opening of epoxides in water

Task specific ionic liquid as a novel and environmental eco-friendly green catalyst has been synthesized and used in the ring opening of epoxides under green conditions. This ionic liquids as solvent, catalyst and reagent afforded the corresponding thiocyanohydrins and azidohydrines with good regioselectivity and very short reaction times. The desired thiocyanohydrins and azidohydrines in 83–93% isolated yields.     

Microwave-assisted synthesis of 3-aminoarylquinolines from 2-nitrobenzaldehyde and indole via SnCl2-mediated reduction and facile indole ring opening

A simple and efficient one-pot two-step synthesis of substituted 3-aminoarylquinolines has been achieved from 2-nitrobenzaldehyde and indoles under microwave irradiation. Firstly 2-nitrobenzaldehydes is reduced to 2-aminobenzaldehyde in situ by commonly used chemo selective reductant SnCl₂ followed by condensation of indole. The acidic nature of the resultant reaction mixture due to SnCl₂ helps in the condensation and facile ring opening of indole leading to the formation of 3-aminoarylquinoline derivatives in good to moderate yields.     

New approach to the synthesis of dibenzodiazacrown ethers by ring transformation of dibenzocrown ether

Opening of the macrocycle of 4′,4″(5″)-dinitrodibenzo-18-crown-6 ethers under the action of MeNH₂ or MeONa to give podands was studied. Structure of the aza podands was confirmed by X-ray diffraction. A new approach to the synthesis of previously unknown dinitrodibenzodiazacrown ethers based on one-step ring transformation of the cis isomer of dinitrodibenzo-18-crown-6 ether on treatment with aliphatic diamines was proposed.     

Selectivity aspects of the ring opening reaction of 2-alkenyl aziridines by carbon nucleophiles

A series of common organometallic reagents were used in the reaction with an acyclic and a cyclic activated 2-alkenyl aziridines and the selectivity aspects for each aziridine was addressed.     

Rapid and efficient ring opening of epoxides catalyzed by a new electron deficient tin(IV) porphyrin

The new electron deficient tin(IV) tetraphenylporphyrinato trifluoromethanesulfonate, [Sn^IV(tpp)(OTf)₂], was used as an efficient catalyst for the alcoholysis, hydrolysis and acetolysis of epoxides. Conversion of epoxides to thiiranes and acetonides were also performed efficiently in the presence of this catalyst.     

New regiocontrolled syntheses of pyrrolopyrazinones and its application to the synthesis of peramine

Two novel regiocontrolled syntheses of pyrrolopyrazinones were developed. N-Methylpyrrole amide and 1-bromo-1-alkyne were annulated in the presence of a copper catalyst to give 3-substituted pyrrolopyrazinone in a regioselective manner. In contrast, heating N-methylpyrrole amide with the same haloalkyne in the presence of K₃PO₄ provided the haloaminal, which was transformed regioselectively into 4-substituted pyrrolopyrazinone. The former procedure was successfully applied to the synthesis of peramine, a natural product isolated from an endophytic fungus.     

Zirconyl nitrate mediated regioselective ring opening of epoxides and aziridines: an easy synthesis of β-nitrato-alcohols and -sulfonamides

Epoxides and aziridines are cleaved efficiently and regioselectively in the presence of zirconyl nitrate at room temperature to afford the corresponding β-nitrato-alcohols and -sulfonamides, respectively, in high yields.     

Hydrolytic ring opening reactions of anhydrides for first row transition metal dicarboxylate complexes

Ring opening reactions of 2,3-pyridine dicarboxylic anhydride are studied with hydrated salts of cobalt, nickel and zinc. The hydrated metal salts preferentially hydrolyze 2,3-pyridine dicarboxylic anhydride rather than causing esterification in methanol medium. Hydrolytic opening of 2,3-pyridine dicarboxylic anhydride by hydrated cobalt(II) acetate and nickel(II) acetate resulted in the corresponding chelate complexes of monodeprotonated 2,3-pyridine dicarboxylic acid. The reaction of copper acetate with pyromellitic dianhydride in the presence of 1,10-phenanthroline gives a dinuclear copper complex whereas a similar reaction with copper(II) chloride gives a mononuclear copper complex.     

Synthesis of Poly(glutamic acid-co-aspartic acid) via Combination of N-carboxyanhydride Ring Opening Polymerization with Debenzylation简

The random copolymers of glutamic acid （LG） and aspartic acid （ASP）, poly（LG-co-ASP）, with designed compositions could be successfully synthesized via combination of N-carboxyanhydride ring opening copolymerization with debenzylation. Ring opening copolymerizations of y：benzyl-L-glutamate N-carboxyanhydride （BLG-NCA） and β-benzyl-Laspartate N-carboxyanhydride （BLA-NCA） were carried out by using different amines including triethylamine （TEA）, diethylamine, n-hexylamine （NHA）, triphenylamine, diphenylamine or aniline as initiators. All the 6 amines were highly efficient to get well-defined poly（BLG-co-BLA） copolymers with designed compositions although the polymerizations proceeded via different mechanisms （normal amine mechanism or/and activated monomer mechanism）, which are based on chemical structure of amines. The molecular weights of poly（BLG-co-BLA） copolymers could be mediated by both TEA concentration and polymerization time. Then, debenzylation ofpoly（BLG-co-BLA） copolymers was conducted to prepare the corresponding hydrophilic random eopolymers of poly（LG-co-ASP） with a-subunit structure in ASP structural units. The contents of LG structural units in poly（LG-co-ASP） copolymers matched with those of BLG-NCA in NCA-monomer feeds in ring opening copolymerizations initiated by NHA or TEA and were closed to the theoretical line. The diblock copolymer of poly（BLG-b-BLA） could also be synthesized via living NCA ring opening copolymerization by sequential addition of BLG- NCA and BLA-NCA.     

Alternative paths in the ring opening of oxadiaziridine: The diimide N-oxide versus the oxodiimide rearrangement

The ring opening of the oxadiaziridine by cleavage of the N-N bond has been theoretically investigated by SCF calculations improved with limited CI. The possible competition of this reaction with the better known ones (N-O bond cleavage, inversion of the N atom) is discussed. The chemical implications of the formation of a new type of 1,3-dipole are examined.     

Metal-free protocol for the synthesis of novel 6-(het)aryl-5-aryl-5H-imidazo[4,5-b][1,2,5]oxadiazolo[3,4-e]pyrazines

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Synthesis of enantiomerically pure 2-(N-aryl,N-alkyl-aminomethyl)aziridines: a new class of ligands for highly enantioselective asymmetric synthesis

A simple and effective synthesis of enantiomerically pure 2-(N-aryl-, N-alkyl-aminomethyl)aziridines from (2S)-N-tritylaziridine-2-carboxylic acid methyl ester has been developed. Treating of this key ester with several primary and secondary amines in the presence of AlMe₃ provided the corresponding chiral N-trityl-2-carboxamides, and their reduction performed with different reagents resulted in the formation of the expected 2-(aminomethyl)aziridines. The choice of reaction conditions allows to either keep or leave the trityl substituent in the product. Such 2-(aminoalkyl)aziridines have shown very high catalytic efficiency in the asymmetric arylation of aldehydes and in other testing asymmetric reactions. On the other hand, homochiral N-trityl-2-carboxamides are interesting building blocks for the synthesis of various biologically active compounds.