Synthesis of 2-amino-3-cyano-4H-chromen-4-ylphosphonates and 2-amino-4H-chromenes catalyzed by tetramethylguanidine

Synthesis of 2-amino-4H-chromen-4-ylphosphonates and 2-amino-4H-chromenes has been accomplished by the reaction of salicylaldehyde, malononitrile, dialkyl/diphenylphosphites catalyzed by 1,1,3,3-tetramethylguanidine (TMG) under neat conditions at room temperature. The applicability of catalytic TMG for the synthesis of 2-amino-4H-chromenes also has been described. The mild reaction conditions, simple work-up procedure, and use of TMG as an inexpensive catalyst provides an economical protocol for the preparation of important phosphorus-containing compounds.     

Synthesis of substituted in benzene ring 4-[(2-aminophenyl)thio]-, 4-[(2-mercaptophenyl)amino]-2-methylquinolines and (4E)-4-[(2-mercaptophenyl)imino]-2-methyl-1,4-dihydroquinolines

By a reaction of 2-methyl-4-chloroquinolines with o-mercaptoaniline under various conditions synteses were performed of substituted in the benzene ring 4-[(2-aminophenyl)thio]-2-methylquinolines and (4E)-4-[(2-mercaptophenyl)imino]-2-methyl-1,4-dihydroquinolines that were respectively by isomerization or rearrangement converted into 4-[(2-mercaptophenyl)amino]-2-methylquinolines.     

Sulphur capture in fluidized bed boilers: The effect of reductive decomposition of CaSO4

Sulphur capture by lime was studied in a 16 MW stationary fluidized bed boiler (FBB). A marked fall-off in sulphur capture was noted at temperatures above about 880 °C. The proposed explanation is that the combustion produces reducing conditions in the particle phase, and thus allows for a reductive decomposition of CaSO₄. This explanation is supported by (i) thermodynamics showing the instability of CaSO₄ under reducing conditions; (ii) in-bed oxygen measurements indicating reducing conditions in the particle phase; (iii) the observed fall-off in sulphur capture with temperature, which is not seen in laboratory tests under oxidizing conditions or in a circulating FBB, where the sorbent particles experience oxidizing conditions to a greater extent; (iv) the observation that the temperature dependence of the sulphur emission is very strong even when the net sulphur capture is zero provided always that CaSO₄ is present and (v) literature data indicating the rate of the proposed reaction.     

Direct comparison of 2,5-di-tert-butyl-1,4-dimethoybenzene and 4-tert-butyl-1,2-dimethoxybenzene as redox shuttles in LiFePO4-based Li-ion cells

2,5-di-tert-butyl-1,4-dimethoxybenzene (DDB) and 4-tert-butyl-1,2-dimethoxybenzene (TDB) have recently been proposed by different research groups as effective redox shuttles for overcharge protection of LiFePO₄-based Li-ion cells. Different test methods used in the published accounts make direct comparison of the merits of DDB and TDB difficult. Here DDB and TDB are tested under the same conditions in Li/LiFePO₄, graphite/LiFePO₄ and Li_4/3Ti_5/3O₄/LiFePO₄ coin-type cells under conditions that approximate those found in practical cells. The results confirm that DDB can support over 200 shuttle-protected overcharge cycles each of 100% cell capacity for all three cell types while TDB can only support between 3 and 15 overcharge cycles. This highlights the importance of testing redox shuttles under conditions that mimic those found in commercial cells.     

An efficient approach for the synthesis of N-Phenylcarboxamido-2-aryl-1,2-dihydro-(4H)-3,1-benzoxazine-4-ones

An efficient synthesis of N-phenylcarboxamodo-2-aryl-1,2-dihydro-(4H)-3,1-benzoxazin-4-ones is described by cyclization reaction of some 2-(benzylidene-amino)-benzoic acids with phenyl isocyanate under reflux conditions in CHCl₃. Higher yields of the products were produced in high purity with simple work-up.     

Synthesis of 4a-carba-β-l-lyxofuranose, 4a-carba-β-l-arabinofuranose and 2,2,5-trimethyl-3a,6a-dihydro-cyclopenta[1,3]dioxol-4-one using Mn/CrCl3 mediated domino reactions and ring closing metathesis

A common method for the synthesis of 4a-carba-β-l-lyxofuranose and 4a-carba-β-l-arabinofuranose from d-mannose and 2,2,5-trimethyl-3a,6a-dihydro-cyclopenta[1,3]dioxol-4-one from d-ribose is described using catalytic Nozaki-Hiyama-Kishi (NHK) conditions and ring closing metathesis (RCM). In this transformation, ω-deoxy-ω-iodo manno/ribo furanoside undergoes reductive elimination in the presence of Mn/CrCl₃ to give the corresponding olefin-aldehyde which was trapped by nucleophile under the same conditions to afford the desired diolefinic species. The ring closing metathesis reaction on these diolefinic species with Grubbs second generation catalyst produced the required carbocycles.     

A new, one-pot, three-component synthesis of 4H-pyrido[1,2-a]pyrimidines, 4H-pyrimido[1,2-a]pyrimidines, and 4H-pyrazino[1,2-a]pyrimidines

A new, one-pot and three-component synthesis of 4H-pyrido[1,2-a]pyrimidines, 4H-pyrimido[1,2-a]pyrimidines, and 4H-pyrazino[1,2-a]pyrimidines is described. The reactive 1:1 zwitterionic intermediate, formed by the addition of isocyanides to dialkyl acetylenedicarboxylates, was trapped by N-(2-heteroaryl)amides to yield a ketenimine intermediate, which was cyclized and then rearranged under the reaction conditions to afford the title compounds under mild reaction conditions in good yields. Single-crystal X-ray analysis conclusively confirms the structure of the obtained bridgehead bicyclic 6-6 heterocyclic compounds.     

An organocatalytic rearrangement of 2-(N-alkyl-/aryl-)amino-4-oxo-4H-1-benzopyran-3-carbaldehyde

2-(Arylamino)-4-oxo-4H-1-benzopyran-3-carbaldehyde rearranges to 4-oxo-4H-1-benzopyran-3-carbanilide when treated with glycine in the presence of formalin, but under similar conditions 2-(alkylamino)-4-oxo-4H-1-benzopyran-3-carbaldehyde rearranges to 3-alkylaminomethylenechroman-2,4-dione.     

Enzyme-catalysed improved resolution of (RS)-4-cyano-4-(3,4-dimethoxyphenyl)-4-isopropyl-1-butanol

Resolutions of (RS)-4-cyano-4-(3,4-dimethoxyphenyl)-4-isopropyl-1-butanol 1 using various enzymes were performed. Among them, Pseudomonas fluorescens resolved it with moderate stereoselectivity (E=13) and reacted faster with the (S)-enantiomer. To optimize enzyme-catalysed reaction conditions for the resolution, the effect of solvents and additives was studied. In n-hexane:ethyl acetate (9:1), both reaction rate and selectivity were high. When pyridine, potassium carbonate and molecular sieves were used as additives, the enantiomeric excess of the (R)-enantiomer was 99, 99 and 98% at 52–60% conversion, respectively. However, in diisopropyl ether, the enantiomeric excess of unreacted alcohol (R)-1 was up to 99% at 70% conversion without additives.     

Synthesis and reactivity of 3-aralkoxy-4-imino-imidazolidin-2-ones: a novel class of 4-iminohydantoins

Reactions of diethylphosphonoalkyl α-aminonitriles with 1,1′-carbonyl-diimidazole or 1,1′-carbonyl-di-(1,2,4-triazole) and O-substituted hydroxylamines under acidic conditions gave 3-alkoxy-4-imino-imidazolidin-2-ones, whereas in presence of triethylamine 4-alkoxy(aralkoxy)imino-imidazolidin-2-ones were formed.     

Synthesis and structure of [2-oxo(thioxo)tetrahydropyrimidin-4-yl]calix[4]arenes

Cone-shaped di- and tetrapropoxycalix[4]arenes functionalized at the upper rim with one or two 2-oxo(thioxo)tetrahydropyrimidine residues were synthesized by the Biginelli reaction of formylcalixarenes with urea (thiourea) and methyl acetoacetate. The steric structure of the products was studied by NMR and X-ray diffraction. The Biginelli reaction with dipropoxyformylcalixarene was diastereoselective, and it quantitatively produced the corresponding meso form. Tetrapropoxydiformylcalixarenes under analogous conditions gave rise to equimolar mixtures of racemic and meso compounds. The macrocyclic skeleton of the synthesized pyrimidine-containing calixarenes in crystal and in solution has a flattened cone conformation. (5-Methoxycarbonyl-2-oxotetrahydropyrimidin-4-yl)calixarene molecules in crystal undergo self-organization to form infinite chains via repeated inclusion of the methoxy group into the cavity of the neighboring macrocycle. Selforganization of bis(5-methoxycarbonyl-2-oxotetrahydropyrimidin-4-yl)calixarene with formation of analogous chains involves intermolecular hydrogen bonding NH ... O=C.     

Calcium acetate catalyzed synthesis of 4-arylidene-2-phenyl-5(4H)-oxazolones under solvent-free conditions

Eight 4-arylidene-2-phenyl-5(4H)-oxazolones (azlactones) have been prepared via Erlenmeyer synthesis from aromatic aldehydes and hippuric acid using calcium acetate under solvent-free conditions with microwave irradiation.     

Synthesis and reactions of 2-hydroxy-4-oxo-4-(2,3,5,6-tetrafluoro-4-methoxyphenyl)-but-2-enoic acid methyl ester

2-Hydroxy-4-oxo-4-(2,3,5,6-tetrafluoro-4-methoxyphenyl)-but-2-enoic acid methyl ester (1) was synthesized by the reaction of pentafluoroacetophenone with dimethyl oxalate in the presence of sodium methylate. Subsequently, reactions of compound 1 with aniline, o-phenylenediamine, and o-aminophenol were investigated. In addition, the thermal cyclization of ester 1 was studied and led to the formation of 5,6,8-trifluoro-7-methoxy-4-oxo-4H-chromene-2-carboxylic acid methyl ester (6) due to nucleophilic substitution of the 3-fluoro group. Hydrolysis of compound 1 and subsequent cyclization by treatment with SOCl₂ gave 5-(2,3,5,6-tetrafluoro-4-methoxyphenyl)-furan-2,3-dione (3). Thermal decarbonylation of compound 3 under mild conditions resulted in the formation of 3-(2,3,5,6-tetrafluoro-4-methoxyphenyl)-propene-1,3-dione (4) which dimerized to pyranone 5.     

Iridium catalysed alkylation of 4-hydroxy coumarin, 4-hydroxy-2-quinolones and quinolin-4(1H)-one with alcohols under solvent free thermal conditions

Ir catalysed alkylation of 4-hydroxy coumarin, 4-hydroxy-2-quinolones and quinolin-4(1H)-one with a range of substituted benzyl and aliphatic alcohols under solvent free thermal conditions afforded the corresponding monoalkylated products in high to excellent yield and in certain cases produced bis-(3,3′-1-methyl-4-hydroxy)methenes.     

Reusable silica-bonded S-sulfonic acid catalyst for three-component synthesis of 2-amino-5-oxo-5,6,7,8-tetrahydro-4H-chromenes and 2-amino-4H-pyrans in aqueous ethanol

Silica-bonded S-sulfonic acid (SBSSA)-catalyzed, facile, one-pot, three-component coupling of 5,5-dimethyl-1,3-cyclohexanedione (dimedone) or 5,5-dimethyl-1,3-cyclohexanedione, aromatic aldehydes, and malononitrile at reflux temperature is described for preparation of 2-amino-5-oxo-5,6,7,8-tetrahydro-4H-chromene derivatives. 2-Amino-3-cyano-6-methyl-4-phenyl-4H-pyran-5-ethylcarboxylate derivatives can also be prepared in good yield under the same experimental conditions by use of ethyl acetoacetate, aldehydes, and malononitrile. The catalyst, silica-bonded S-sulfonic acid, was reused and recycled without any loss of activity or product yield.     

Synthesis and reactions of pyrazole-4-carbaldehydes

1-, 3-, and 5-Alkylpyrazoles, as well as linearly bridged bis-pyrazoles, were converted into the corresponding 4-formyl derivatives by Vilsmeier-Haak reaction both under standard conditions and under microwave activation in DMF over a period of 10 min. 1,1′-(Hexane-1,6-diyl)bis(3,5-dimethyl-1H-pyrazole) and 1,1′-(benzene-1,4-diyldimethylene)bis(3,5-dimethyl-1H-pyrazole) gave rise to 4-formyl derivatives at both pyrazole rings. 5-Chloro-1,3-dialkyl-1H-pyrazoles failed to undergo formylation according to Vilsmeier-Haak or under microwave activation. 1,1′-Bridged bis-3,5-dimethyl-1H-pyrazoles reacted with 2-sulfanylethanol on heating in the presence of chloro(trimethyl)silane to give the corresponding bridged bis-4-(1,4,6-oxadithiocan-5-yl)-1H-pyrazoles.     

A new synthetic approach to 5-dethia-4-methyl-5-oxacephems

Starting from (l)-ethyl lactate and 4-vinyloxy-azetidin-2-one the diastereomeric (4S,6R)- and (4S,6S)-4-methyl-5-oxa-3-methylene and 3-oxo-cephams were obtained. The formation of the cepham skeleton proceeds with a diastereomeric excess up to 80%, depending on catalyst and reaction conditions. For comparison, the corresponding racemic cephams lacking a methyl at C-4 or with a gem-dimethyl group at C-4 were synthesized.     

Hydrothermal synthesis and crystal structure of a new ammonium gallium hydroxyphosphate (NH4)Ga(OH)PO4

A new ammonium gallium hydroxyphosphate (NH₄)Ga(OH)PO₄ was synthesized under mild hydrothermal conditions (200°C, τ = 168 h). The equimolar content of Ga and P was determined by chemical analysis and electron probe X-ray microanalysis. The presence of NH₄ and OH groups was demonstrated by IR and Raman spectroscopy. An ab initio model of the crystal structure was refined by the Rietveld method (space group P2₁/m, Z = 2): a = 4.4832(1) Å, b = 6.0430(1) Å, c = 8.5674(1) Å, β = 98.019(1)°, R _p = 0.0552, R _wp = 0.0723. A zero SHG signal (T = 300 K) confirmed a centrosymmetric structure of the compound. The structure contains layers composed of GaO₄(OH)₂ octahedra and PO₄ tetrahedra. The interlayer space accommodates ammonium cations. The layer is based on linear chains of edge-sharing GaO₄(OH)₂ octahedra with a zigzag trans-arranged-Ga-(OH)-Ga-(OH)-backbone. The construction of the layer in (NH₄)Ga(OH)PO₄ was found to be topologically related to that in (En)_0.5Fe(OH)PO₄. The effect of the gradual F^? → OH^? substitution in the quasi-morphotropic series (NH₄)GaF_1-δ(OH)_δPO₄ (δ = 0, 0.5, 1.0) on the degree of polarization of the mixed anionic radical was considered. (NH₄)Ga(OH)PO₄ is thermally unstable: removal of NH₃ and H₂O molecules in the range 170–450°C is accompanied by the formation of two polymorphs of GaPO₄.     

CuI-Catalyzed Coupling Reactions of 4-Iodopyrazoles and Alcohols: Application toward Withasomnine and Homologs

The direct 4-alkoxylation of 4-iodo-1H-pyrazoles with alcohols was achieved by a CuI-catalyzed coupling protocol. The optimal reaction conditions employed excess alcohol and potassium t-butoxide (2 equiv) in the presence of CuI (20 mol%) and 3,4,7,8-tetramethyl-1,10-phenanthroline (20 mol%) at 130 °C for 1 h under microwave irradiation. The present method was efficiently applied to the synthesis of withasomnine and its six- and seven-membered cyclic homologs.     

An efficient approach to isoindolo[2,1-b][2]benzazepines via intramolecular [4+2] cycloaddition of maleic anhydride to 4-α-furyl-4-N-benzylaminobut-1-enes

Acylation of 4-α-furyl-4-N-benzylaminobut-1-enes with maleic anhydride gave 4-oxo-3-aza-10-oxatricyclo[5.2.1.0^1,5]dec-8-ene-6-carboxylic acid via amide formation followed by intramolecular Diels-Alder reaction of furan (IMDAF). The cycloaddition proceeded under mild reaction conditions (25 °C) and provided only the exo-adduct in quantitative yield. Treatment of this compound with PPA gave isoindolo[2,1-b][2]benzazepine derivatives via ring opening, aromatization and intramolecular electrophilic alkylation. In order to extend the scope of the reaction sequence, 7-oxo-5,11b,12,13-tetrahydro-7H-isoindolo[2,1-b][2]benzazepine-8-carboxylic acids were further transformed into useful synthetic intermediates.