Addition Reaction Between Trimethyl Phosphite and Dibenzoylacetylene in the Presence of SH- or NH-Acids

The reactive 1:1 intermediate produced in the addition reaction between trimethyl-phosphite and dibenzoylacetylene was trapped by SH- or NH-acids such as 4-nitroimidazole, 4-methyl-5-nitroimidazole, succinimide, or mercaptoacetic acid to produce 2-substituted 1,4-diphenylbutane-1,4-diones.     

Synthesis of Functionalized Pyrroles by Reaction of 3,4‐Diacetylhexane‐2,5‐dione with Primary Amines in Water

3,4‐Diacetylhexane‐2,5‐dione (tetra‐acetylethane) undergoes a complex reaction with primary amines in boiling water to produce N‐alkyl‐3‐acetyl‐2,5‐dimethylpyrroles, together with small quantities of N‐alkyl‐3,4‐diacetyl‐2,5‐dimethylpyrroles and 2,5‐dimethyl‐1H‐pyrrol‐3‐yl‐vinyl‐acetamides. When the reaction was carried out in methanol at room temperature, the yields of the latter products increased.     

Reaction between alkyl isocyanides and isopropylidene Meldrum’s acid in the presence of bidentate nucleophiles

Summary The reaction between alkyl isocyanides and isopropylidene Meldrum’s acid in the presence of 1,2-ethanediol leads to N ¹-(alkyl)-2-(5,7-dioxo-1,4-dioxepane-6-yl)-2-methylpropanamides. 1,3-Propanediol or 1,4-butanediol produce hydroxyalkyl 1-(tert-butyl)-4,4-dimethyl-2,5-dioxo-3-pyrrolidinecarboxylates. When the reaction was performed in the presence of catechol, bis(2-hydroxyphenyl) 2-[2-(tert-butylamino)-1,1-dimethyl-2-oxoethyl]malonate was obtained. 2-Aminophenols react with alkyl isocyanides in the presence of isopropylidene Meldrum’s acid to produce 1-alkyl-N ³-(2-hydroxyaryl)-4,4-dimethyl-2,5-dioxo-3-pyrrolidinecarboxamides in good yields.     

Exact Solution of Petrov Type {3,1} Metric via Time Dependent Quasi-Maxwell Equations

In this paper, we show that how to apply the time dependent quasi-Maxwell equations for exact solution of Einstein field equations in vacuum for Petrov type {3,1} metric.     

13C and 77Se NMR spectra of thienoisoselenazoles,selenoloisothiazoles, selenoloisoselenazoles and thienoisothiazoles

Measurements are reported of NH exchange rates of urea, thiourea, acetamide and thioacetamide, using line-shape analysis with natural-abundance ¹⁵N NMR spectra. Base-catalyzed NH-proton exchange of thiourea is 30–40 times faster than for urea, while the corresponding acid-catalyzed exchange is 150 times slower. The base-catalyzed proton exchange for thioacetamide is about 1000 times faster than that of acetamide at 25°C, while the corresponding acid-catalyzed exchange is some 260 times slower.     

Carbon-13 nuclear magnetic resonance spectra and conformations of cis,cis-1,5-cyclooctadiene monoepoxide and cis,syn,cis-1,5-cyclooctadiene diepoxide

The natural-abundance ¹³C NMR spectra of cis,cis-1,5-cyclooctadiene monoepoxide and cis,syn,cis-1,5-cyclooctadiene diepoxide have been investigated over the temperature range of – 10 to – 180°C. Whereas the spectra of the former showed no dynamic NMR effect, two different conformations in the ratio of 3:1 were observed at low temperatures for the latter. The free-energy barrier (ΔG^≠) for conversion of the major conformation to the minor conformation is calculated to be 5.9°0.2 kcal mol^?1 from a line-shape analysis of spectra obtained at intermediate temperatures. It is shown that cis,syn,cis-1,5-cyclooctadiene diepoxide exists in solution in chair (major) and in twist-boat (minor) conformations of slightly different energies. Interconversion paths between these conformations are discussed. The monoepoxide is suggested to have a twist-boat conformation that is rapidly pseudorotating via a boat conformation even at – 180°C.     

13C NMR spectra of benzofuroxan and related compounds

The ¹³C n.m.r. spectrum of benzofuroxan at ?15°C is assigned on the basis of selective decoupling experiments and by comparison with the ¹³C chemical shifts of model compounds. The ¹³C spectra were also measured in trifluoroacetic acid as a solvent. From the temperature dependence of the ¹³C spectrum of benzofuroxan in CDCl₃, a barrier of 14·0 ± 0·2 kcal mol^?1 is obtained for the degenerate tautomerism in this compound.     

A Simple Synthesis of Stable 1,4-Diionic Pyridinium Betaines

 Protonation of the reactive intermediate produced in the reaction between pyridine and dialkyl acetylenedicarboxylates by strong CH-acids such as N,N′-dimethylbarbituric acid, Meldrum’s acid, or indane-1,3-dione leads to a vinylpyridinium cation which undergoes an addition reaction with the enolate anion of the CH-acid to produce stable 1,4-diionic pyridinium betaines in good yields.