A convenient synthesis of linear pyranocoumarins. Xanthyletin and 3-Phenylxanthyletin

A convenient synthesis of linear pyranocoumarins, viz., 8,8-dimethyl-2H,8H-benzo[1,2-b; 5,4-b]dipyran-2-one (xanthyletin,1) and 8,8-dimethyl-3-phenyl-2H,8H-benzo[1,2-b; 5,4-b]dipyran-2-one (3-phenylxanthyletin,2) is described. The key steps are blocking the 8-position of appropriate 7-hydroxy-2H-1-benzopyran-2-one derivatives with iodine and 1,1-dimethyl-2-propynylation followed by cyclisation.

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Ein einfacher Syntheseweg zu linearen Pyranocumarinen. Xanthyletin und 3-Phenylxanthyletin

Zusammenfassung Es wird ein vorteilhafter Weg zur Synthese von linearen Pyranocumarinen am Beispiel von Xanthyletin und 3-Phenylxanthyletin gezeigt. Das Syntheseprinzip besteht in einer Blockierung der 8-Position des entsprechenden 7-Hydroxy-2H-1-benzopyran-2-ons mit Jod und einer 1,1-Dimethyl-2-propinylierung mit nachfolgender Cyclisierung.

     

Condensation of 4-aryl-4-oxobutanoic acids with benzylamines: Synthetic and structural studies on 1-arylmethyl-3-[(<Emphasis Type="Italic">E</Emphasis>)-1-arylmethylidene]-5-phenyl-2,3-dihydro-1H-2-pyrrolones

The microwave-mediated reaction of 4-aryl-4-oxobutanoic acids with benzylamines furnished 1-arylmethyl-3-[(E)-1-arylmethylidene]-5-phenyl-2,3-dihydro-1H-pyrrolones. This result is in contract to the earlier report on this reaction conducted under neat conditions. Structures for the products were assigned on the basis of spectral data and confirmed by independent synthesis. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 368–373, March, 2007.     

The complexes of aluminium,gallium, and indium with calmagite: Evaluation of stepwise stability constants

Summary Calmagite [1-(1-hydroxy-4-methyl-2-phenyl azo)-2-naphthol sulphonic acid], dissociates in two steps. It forms violet complexes with Al³⁺, Ga³⁺ and In³⁺. The stepwise proton-ligand stability constants of calmagite and stepwise metal-ligand stability constants of these complexes were evaluated by potentiometric titration technique ofBjerrum andIrving andRossotti. The order of the stabilities of complexes is In³⁺ > Ga³⁺ > > Al³⁺.

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Zusammenfassung Camalgit [1-(1-Hydroxy-4-methyl-2-phenylazo)-2-naphtholsulfonsäure] dissoziiert in zwei Stufen und bildet violette Komplexe mit Al(III), Ga(III) und In(III). Die Konstanten der Dissoziationsstufen der freien Säure und die der Metallkomplexe wurden potentiometrisch nachBjerrum bzw.Irving undRossotti ermittelt. Die Stabilität der Komplexe nimmt in der Reihe In(III) > Ga(III) > Al(III) ab.

     

13C NMR/DFT/GIAO studies of phenylene bis(1,3-dioxolanium) dications and 2,4,6-triphenylene tris(1,3-dioxolanium) trication

The o-, m-, and p-phenylene bis(1,3-dioxolanium) dications (4-6) and 2,4,6-triphenylene tris(1,3-dioxolanium) trication (7) have been prepared by the ionization of the corresponding 2-methoxyethyl benzoates in FSO(3)H or CF(3)SO(3)H at 40 and 60 degrees C, respectively. The charge delocalization in these carbocations was probed by (13)C NMR chemical shifts and substantiated by GIAO/DFT calculations. Relatively less charge is delocalized into the aromatic ring of the carbotrication 7. The rotational barrier around the C(+)-Ar bond for carbodications 4 and 5 was also estimated to be 8-10 kcal/mol.     

Reactions of titanium(IV) isopropoxide with aliphatic and aromatic hydroxy esters,part I. 5-, 6-, 7- and 8-coordinate titanium(IV) complexes

Summary Reactions of titanium(IV) isopropoxide with ethyl 1-hydroxycyclohexylacetate, ethyl 2-hydroxy-2-arylpropionate, ethyl 2-hydroxy-2-arylbutyrate and ethyl 2-hydroxy-2-arylhydrocinnamate have been studied in dry benzene in different molar ratios under strictly anhydrous conditions. The Ti(OPr-i)₄-_nL_n type compounds, where L = hydroxy ester and n = 1 to 4, have been isolated and characterised by elemental analysis, molecular weight, i.r. and n.m.r. spectral studies. These products may be distilled unchanged under reduced pressure.Reprints of this are not available.     

P and H NMR studies of the transesterification polymerization of polyphosphonate oligomers

Polymeric phosphonate esters are an interesting class of organophosphorus polymers because both the polymer backbone and phosphorus substituents can be modified. These polymers have been prepared by ring-opening polymerizations of cyclic phosphites, stoichiometric polycondensations of dimethyl phosphonate with diols in conjunction with diazomethane treatment and by transesterification of polyphosphonate oligomers. Our initial attempts to prepare high molecular weight polymeric phosphonate esters by the transesterification methods were unsuccessful. Results indicate that the reactions of dimethyl phosphonate with diols to form polyphosphonate oligomers with only methyl phosphonate end groups are plagued by a serious side reaction that forms phosphonic acid end groups. These end groups do not participate in the transesterification reaction and limit the molecular weights of the polymers that can be obtained. The phosphonic acid end groups can be converted into reactive methyl phosphonate end groups by treatment with diazomethane, however diazomethane is explosive and the polymerization is slow. An alternative route for the production of high molecular weight polymers is the transesterification of the 1,12-bis(methyl phosphonato)dodecane, formed by the reaction of excess dimethyl phosphonate and 1,12-dodecanediol, with a Na₂CO₃ promoter. This allows polymers with molecular weights of up to 4.5×10⁴ to be prepared, and no phosphonic acid end groups are observed in these polymers. Thermal analyses of the poly(1,12-dodecamethylene phosphonate) have shown that this polymer has reasonable thermal stability (onset of thermal decomposition at 273 °C). This polymer also undergoes a cold crystallization process at 15 °C similar to that which has been observed in some polyesters, polyamides and elastomers.     

alpha-thiocyanation of carbonyl and beta-dicarbonyl compounds using (dichloroiodo)benzene-lead(II) thiocyanate

The combination reagent (dichloroiodo)benzene and lead(II) thiocyanate in dichloromethane effects oxidation of various enol silyl ethers, ketene silyl acetals, and beta-dicarbonyl compounds, thereby providing an efficient and convenient method for alpha-thiocyanation of carbonyl and beta-dicarbonyl compounds.     

Determination of cadmium by electrothermal atomic absorption spectrometry after microwave-assisted digestion of animal tissues and sewage sludges

The determination of cadmium in different sample types has been carried out by electrothermal atomization atomic absorption spectrometry with D(2)-background correction using a unpyrocoated graphite tube, after pressurized microwave-assisted digestion. Five chemical modifiers [(NH(4))(2)HPO(4), Pd(NO)(3))(2), Ni(NO(3))(2), thiourea and Triton X-100] have been assayed and nickel nitrate has been found to be most effective for an accurate determination of cadmium in mussel tissue, pig kidney and sewage sludge. The characteristic mass of the method is of the order of 1 pg and the limit of detection is lower than 0.1 ng/ml.     

Spectrophotometric and potentiometric studies of oxovanadium(IV) chelates with Eriochrome black T and Solochrome black 6 BN

Vanadium(IV) forms colored chelates with Erio T and Solo 6 BN (λ_max 570 and 580 nm, respectively) at pH 3.8. The composition MR₂ of the chelates investigated was established by continuous variation, mole ratio, slope ratio and straight-line methods spectrophotometrically. For photometric determination of V(IV) with these reagents Sandell's sensitivity, Beer's law range, Ringbom optimum range were also determined. Bjerrum and Calvin potentiometric titration technique was employed to determine the stepwise formation constants of each system. For V(IV)-Erio T system values of log K₁ = 14.4, log K₂ = 10.9 and for V(IV)-Solo 6 BN system log K₁ = 16.1, log K₂ = 11.8 were obtained.