Synthesis of (R)-3,4-dihydro-2H-pyran-2-carboxaldehyde: application to the synthesis of potent adenosine A2A and A3 receptor agonist

Synthesis of potent adenosine A_2A and A₃ receptor agonist from the modification of adenosine-5′-N-ethylcarboxamide (NECA) has been reported. Diastereoisomer possessing an (R)-3,4-dihydro-2H-pyranyl (DHP) moiety exhibited the highest affinity at the A_2A and A₃ receptors. The key steps involve the synthesis of (R)-3,4-dihydro-2H-pyran-2-carboxaldehyde (7), which was obtained through the enzyme-catalyzed kinetic resolution of (±)-2-acetoxymethyl-3,4-dihydro-2H-pyran (5).     

Synthesis, spectral characterization, and crystal structure of mononuclear mercury(II) complex [Hg((3,4-MeO-Bza)2En)I2]

Mercury(II) complex, [Hg((3,4-MeO-Bza)₂En)I₂] (I), where (3,4-MeO-Bza)₂En = N,N′-bis(3,4-dimethoxybenzaldehyde)ethylenediimine, has been synthesized from the reaction of HgI₂ with (3,4-MeO-Bza)₂En in methanol as solvent at 50°C. It was characterized by elemental analysis (CHN), ¹H-NMR spectroscopy and confirmed by single-crystal X-ray diffraction analysis. The complex I crystallizes in the monoclinic system, with space group P2₁/c, having one symmetry-independent Hg²⁺ ion coordinated in a distorted tetrahedral geometry by two N atoms of the Schiff base ligand and by two I atoms. The Schiff base ligand (3,4-MeO-Bza)₂En acts as a chelating ligand and coordinates via two N atoms to the mercury center. It adopts an (E, E) conformation.     

Fluorocarbohydrates-XXVIII: Synthesis and characterisation of 2-deoxy-2-fluoro-derivatives of l-rhamnose and l-epirhamnose

Addition of CF₃OF to 3,4-di-O-acetyl-l-rhamnal gave four products separable by fractional crystallisation and column chromatography. The two principal products were in the epirhamnose series, i.e. trifluoromethyl 3,4-di-O-acetyl-2,6-dideoxy-2-fluoro-α-l-glucoside and 3,4-di-O-acetyl-2,6-dideoxy-2-fluoro-α-l-glucosyl fluoride. The lesser products were in the rhamnose series viz. trifluoromethyl 3,4-di-O-acetyl-2,6-dideoxy-2-fluoro-β-1-mannoside and 3,4-di-O-acetyl-2,6-dideoxy-2-fluoro-β-l-mannosyl fluoride. The structures were confirmed by ¹H and ¹⁹F NMR spectral measurements. Deacylation and acidic hydrolysis gave the free 2-deoxy-2-fluoro sugars of both series.     

Nucleophilic cyclization of 3-alkynylquinoxaline-2-carbonitriles into pyrido[3,4-b]quinoxalines

3-Alkynylquinoxaline-2-carbonitriles have been synthesized from 3-chloroquinoxaline-2-carbonitrile via the Sonogashira reaction. Treatment of 3-alkynylquinoxaline-2-carbonitriles with an alkylamine or ammonia has been shown to produce stable enamines, e.g., (Z)-3-(2-aryl-2-aminovinyl)quinoxaline-2-carbonitriles. Their base-induced cyclization gave the previously unknown pyrido[3,4-b]quinoxalin-1(2H)-imines or pyrido[3,4-b]quinoxalin-1-amines. 3-Alkynylquinoxaline-2-carbonitriles were directly transformed into pyrido[3,4-b]quinoxalin-1(2H)-imines by heating with an alkylamine and K₂CO₃ in DMF. The ionization constants, and absorption and fluorescent properties of the resulted pyrido[3,4-b]quinoxalin-1(2H)-imines were measured.     

Synthesis, structures and magnetic properties of two 3D 3,4-pyridinedicarboxylate bridged manganese(II) coordination polymers incorporating 1D helical Mn(carboxylate)2 chain or Mn3(OH)2 chain

The hydrothermal reactions of MnCl₂·4H₂O, 3,4-pyridinedicarboxylic acid (3,4-pydaH₂) and triethylamine in aqueous medium yield two 3D metal-organic hybrid materials, [Mn(3,4-pyda)] (1) and [Mn₃(OH)₂(3,4-pyda)₂(H₂O)₂] (2), respectively. In both complexes, each 3,4-pyda acts as a pentadentate ligand to connect five Mn(II) atoms via the pyridyl group and the two μ₂-carboxylate groups (one in syn,anti-mode and one in syn-syn mode for 1 and both in syn,anti-mode for 2). Complex 1 possesses an interesting 3D coordination polymeric structure incorporating 1 D helical Mn(μ₂-carboxylate)₂ chain units, in which each Mn(II) atom is coordinated in less common square pyramidal geometry to four carboxylato oxygen atoms and one pyridyl nitrogen atom. Each 3,4-pyda links three helical Mn(μ₂-carboxylate)₂ chains and each Mn(μ₂-carboxylate)₂ chain is linked by other eight helical Mn(μ₂-carboxylate)₂ chains via sharing 3,4-pyda bridges. Complex 2 is a 3D coordination network consisting of 1D Mn₃(OH)₂ chains and 3,4-pyda bridges. The repeating trimeric structural unit in the manganese(II) hydroxide chain consists of two edge-sharing symmetry-related manganese octahedra linked via μ₃-OH to a vertex of Mn₂ octahedron. Each 3,4-pyda links three Mn₃(OH)₂ chains and each Mn₃(OH)₂ chain is linked by other six Mn₃(OH)₂ chains via 3,4-pyda bridges, resulting in a 3D coordination solid. Magnetic measurements reveal that a weak antiferromagnetic interaction between the Mn^II ions occurs in complex 1 and a 3D magnetic ordering at about 7.0 K in complex 2.     

Oxidative transformations of 6-trifluoromethyl-2H-thiopyran as a route to fluoro-containing thiopyranosides

The synthesis of cis- and trans-6-(trifluoromethyl)-3,4-dihydro-2H-thiopyran-3,4-diols from 6-(trifluoromethyl)-2H-thiopyran via an OsO₄-catalysed dihydroxylation and bromohydroxylation-alkaline hydrolysis sequence is described. Acetylation of the diols followed by S-oxidation affords the corresponding cis- and trans-3,4-diacetoxy-6-(trifluoromethyl)-3,4-dihydro-2H-thiopyran S-oxides which reacted with acetic anhydride and boron trifluoride diethyl ether complex by an additive Pummerer pathway giving tetraacetyl derivatives of trifluoromethyl-containing thiopyranoses.     

Synthesis of 2-(1-aminocyclopropyl)pyrrolidine-3,4-diol derivatives applying titanium-mediated reaction conditions

The titanium-mediated cyclopropanation reaction using Ti(OⁱPr)₃Me/EtMgBr/BF₃·OEt₂ has been applied to various 2-cyanopyrrolidines for the synthesis of functionalized 2-(1-aminocyclopropyl)pyrrolidine-3,4-diol derivatives (dideoxyiminoalditols). Under the same experimental conditions the trans-5-azidomethyl-2-cyanopyrrolidine derivative was not cyclopropanated but reduced into the corresponding 5-amino-2-cyano derivative. After polyol deprotection 2-(1-aminocyclopropyl)pyrrolidine-3,4-diols were obtained and their inhibitory activity towards 13 glycosidases has been evaluated. (2S,3S,4R,5S)-2-(1-Aminocyclopropyl)-5-methylpyrrolidine-3,4-diol (38), which has the same absolute configuration as l-fucose, is a moderate (IC₅₀=44 μM), but selective, inhibitor of α-l-fucosidase from human placenta.     

2-Alkoxy-3,4-dihydropyrans as modular substrates to construct polyheterocycles by reacting with NH2-containing bisnucleophiles

2-Alkoxy-3,4-dihydropyrans were proved to be a class of powerful modular substrates to construct polyheterocycles by reacting with NH₂-containing dinucleophiles, such as anthranilamide, 2-aminobenzenethiol, 1-(2-aminophenyl)pyrrole, and 2-(o-aminophenyl)indole in the presence of LiBr·H₂O. A three-component reaction of isatoic anhydride, 2-alkoxy-3,4-dihydropyran and amine was also developed as well.     

Convenient access to sterically hindered C2 chiral 2,2,5,5-tetraphenyltetrahydrofuran-3,4-diols: intramolecular selective 1,4-cyclocondensation of (2R,3R)- and (2S,3S)-1,1,4,4-tetraphenylbutanetetraols

Sterically hindered C₂ chiral (3R,4R)- and (3S,4S)-2,2,5,5-tetraphenyltetrahydrofuran-3,4-diols have been conveniently prepared in a very high yield via heterogeneous intramolecular selective 1,4-cyclocondensation of (2R,3R)- and (2S,3S)-1,1,4,4-tetraphenylbutanetetraol in concentrated hydrohalic acids, respectively. Preliminary examination of additives for the Barbas–List reaction showed that in certain cases, the hindered C₂ chiral tetrahydrofuran-3,4-diols were better chiral auxiliaries than enantiopure (R)- and (S)-1,1′-bi-2-naphthols.     

ZrCl4 or ZrOCl2 under neat conditions: optimized green alternatives for the Biginelli reaction

Biginelli reactions were performed using either ZrCl₄ or ZrOCl₂·8H₂O as catalysts under neat conditions. Shorter reaction time than most of the classical methods was required when ZrCl₄ was used. In general, 3,4-dihydropyrimidin-2(1H)-ones and thioxo-3,4-dihydropyrimidin-2(1H)-ones were obtained under neat conditions in moderate to good yields and good purity without using harmful solvents in the work up.     

Ru(II)-Catalyzed rearrangement of 2-aryl-2-(phenylthio)penta-3,4-dienyl 2,2,2-trichloroacetimidates

[RuCl₂(p-cymene)]₂ efficiently catalyzes the rearrangement of 2-aryl-2-(phenylthio)penta-3,4-dienyl 2,2,2-trichloroacetimidate to afford (Z)-2,2,2-trichloro-N-(4-aryl-1-(phenylthio)penta-2,4-dien-2-yl)acetamide. Ru carbene is assumed as the reactive intermediate in this rearrangement.     

A practical and efficient procedure for reduction of carboxylic acids and their derivatives: use of KBH4-MgCl2

The use of KBH₄-MgCl₂ to reduce carboxylic acids and their derivatives to the corresponding alcohols or the respective reduced products is described. Methyl (S)-3,4-O-isopropylidene-3,4-dihydroxy butanoate 2 used as a reference substrate was reduced with KBH₄ and MgCl₂ in 1:1 mol ratio to (S)-1,2-O-isopropylidene-1,2,4-butanetriol 1.     

Synthesis of substituted 4-(3-alkyl-1,2,4-oxadiazol-5-ylmethyl)-3,4-dihydro-2H-1,4-benzoxazines and 4-(1H-benzimidazol-2-ylmethyl)-3,4-dihydro-2H-1,4-benzoxazines

Substituted 2H-1,4-benzoxazines were synthesized from substituted 2-amino phenols and 1,2-dibromoethane using K₂CO₃ in good to excellent yields. The cyclized products were further reacted with alkyl bromides to obtain the desired N-substituted 3,4-dihydro-2H-1,4-benzoxazines.     

Superelectrophilic activation of N-aryl amides of 3-arylpropynoic acids: synthesis of quinolin-2(1H)-one derivatives

The superelectrophilic activation of N-aryl amides of 3-arylpropynoic acids by Bronsted superacids (CF₃SO₃H, HSO₃F) or strong Lewis acids AlX₃ (X=Cl, Br) results in the formation of 4-aryl quinolin-2(1H)-ones in quantitative yields. The vinyl triflates or vinyl chlorides may be formed as additional reaction products. The investigated amides in reactions with benzene give 4,4-diaryl 3,4-dihydroquinolin-2-(1H)-ones under the superelectrophilic activation. 4-Aryl quinolin-2(1H)-ones in POCl₃ are converted into 4-aryl 2-chloroquinolines. 4-Fluorophenyl-4-phenyl 3,4-dihydroquinolin-2-(1H)-one give N-formylation products in a yield of 79% under the Vilsmeier–Haack reaction conditions.     

1,3-Dipolar cycloaddition of 2- and 3-nitroindoles with azomethine ylides. A new approach to pyrrolo[3,4-b]indoles

The 1,3-dipolar cycloaddition of unstabilized azomethine ylides with 2- and 3-nitroindoles furnishes the expected hexahydropyrrolo[3,4-b]indole cycloadducts in good to excellent yields. The cycloadducts can be denitrated with Bu₃SnH/AIBN, and cycloadduct 5 was oxidized with MnO₂ to yield the known pyrrolo[3,4-b]indole 13.     

4-Substituted 5-nitroisoquinolin-1-ones from intramolecular Pd-catalysed reaction of N-(2-alkenyl)-2-halo-3-nitrobenzamides

4-Methyl- and 4-benzyl-5-aminoisoquinolin-1-ones are close analogues of the water-soluble PARP-1 inhibitor 5-AIQ. Their synthesis was approached through Pd-catalysed cyclisations of N-(2-alkenyl)-2-iodo-3-nitrobenzamides. Reaction of N,N-diallyl-2-iodo-3-nitrobenzamide with Pd(PPh₃)₄ gave a mixture of 2-allyl-4-methyl-5-nitroisoquinolin-1-one and 2-allyl-4-methylene-5-nitro-3,4-dihydroisoquinolin-1-one. N-Benzhydryl-N-cinnamyl-2-iodo-3-nitrobenzamide similarly gave 2-benzhydryl-4-benzyl-5-nitroisoquinolin-1-one and 2-benzhydryl-4-benzylidene-5-nitro-3,4-dihydroisoquinolin-1-one. The isomeric products are not interconvertible. A deuterium-labelling study indicated that the isomers were formed by different pathways: a π-allyl-Pd route and the classical Heck route. The corresponding secondary amides N-allyl-2-iodo-3-nitrobenzamide and N-((substituted)-cinnamyl)-2-iodo-3-nitrobenzamide gave good yields of the required 4-methyl- and 4-((substituted)-benzyl)-5-nitroisoquinolin-1-ones, respectively, under optimised conditions (Pd(PPh₃)₄, Et₃N, Bu₄NCl, 150 °C, rapid heating). Hydrogenation of the nitro groups gave 4-methyl- and 4-benzyl-5-aminoisoquinolin-1-ones, which were potent inhibitors of PARP-1 activity.     

Visible-light-induced chemoselective reactions of quinoxalin-2(1H)-ones with alkylboronic acids under air/N2 atmosphere

A visible-light-induced chemoselective reactions of quinoxalin-2(1H)-ones with alkylboronic acids in the presence of air (O₂) and N₂ atmosphere was developed under transition-metal free conditions, providing 3-alkylquinoxalin-2(1H)-ones and 3,4-dihydroquinoxalin-2(1H)-ones, respectively. The overall strategy accommodates a broad scope of substituted quinoxalin-2(1H)-ones and alkylboronic acids with good to excellent product yields.     

An unusual oxidation-dealkylation of 3,4-dihydropyrimidin-2(1H)-ones mediated by Co(NO3)2·6H2O/K2S2O8 in aqueous acetonitrile

4-Aryl-6-methyl-3,4-dihydropyrimidin-2(1H)-one (DHPM) scaffolds of Biginelli type were oxidized using Co(II)/S₂O₈²⁻ and the reaction afforded 6-unsubstituted pyrimidin-2(1H)-ones through an unprecedented dealkylation process. 4-Alkyl DHPMs under similar conditions afforded yet another unusual product, ethyl tetrahydropyrimidin-2,4(1H,3H)-dione-5-carboxylate.     

Alkenyl derivatives of 5-nitro-2-pyridone: Synthesis and halocyclization

Alkylation of 5-nitro-2-pyridone by alkenyl halides in acetone in the presence of K₂СО₃ proceeds with generation of a mixture of N- and О-derivatives with N-isomer prevailing. 1-Allyl- and 1-methylallyl-5-nitro-2-pyridone react with halogens with the formation of 2-halomethyl-6-nitro-2,3-dihydrooxazolo[3,2-a]-pyridinium halides. 1-Prenyl-5-nitro-2-pyridone reacts with bromine with the formation of 3-bromine-2,2-dimethyl-7-nitro-3,4-dihydro-2Н-pyrido[2,1-b][1,3]oxazinium bromide, and with iodine giving 2,2-dimethyl-7-nitro-3,4-dihydro-2Н-pyrido[2,1-b][1,3]oxazinium triiodide.     

Synthesis, crystal structure and properties of two 1D nano-chain coordination polymers constructed by lanthanide with pyridine-3,4-dicarboxylic acid and 1,10-phenanthroline

The hydrothermal reactions of LnCl₃·6H₂O (Ln=Eu, Tb), pyridine-3,4-dicarboxylic acid (3,4-pydaH₂), 1,10-phenthroline (phen) and NaOH in aqueous medium yield two metal-organic hybrid materials, [Eu₂(3,4-pyda)₃(phen)(H₂O)·H₂O]_n (1) and [Tb₂(3,4-pyda)₃(phen)(H₂O)·H₂O]_n (2), respectively. Both compounds have similar topology structure containing one-dimensional nano-chain, which is further assembled into a three-dimensional supramolecular network via π-π stacking interactions and hydrogen bonds. To the best of our knowledge, they represent the first example of nano-chain coordination polymers constructed by 3,4-pydaH₂ and chelate heterocylic ligand. Interestingly, the 3,4-pyda anion exhibits three kinds of coordination modes in these complexes. The coordination modes of 3,4-pyda in complexes 1 and 2 have not been observed in other coordination polymers containing 3,4-pyda ligands. Compounds 1 and 2 exhibit strong fluorescent emission bands in the solid state at room temperature. Their magnetic analyses show that they exhibit different magnetic interactions.