Ahmad Q. Hussein

Heterocycles from Nitrile Imines. Part IV. Chiral 4,5-Dihydro-1,2,4-triazin-6-ones

The reaction of nitrile imines (II) with α-amino esters (III) proceeds with no detectable racemization and constitutes a convenient synthetic route to 4,5-dihydro-1,2,4-triazin-6-ones (IV). Permanganate oxidation of the heterocycles (IV) affords the corresponding 1,2,4-triazin-6-ones (V). The reaction of (II) with β-amino esters gives the respective acyclic amidrazone adducts (VI)

Highly active and selective catalysts for olefin hydrosilylation reactions using metalloporphyrins intercalated in natural clays

Tetra(4-pyridyl)porphyrinato-manganese(III) (MnTPyP+) ions intercalated inside nano- and micro-size natural clay powders effectively catalyzed the hydrosilylation reaction of 1-octene and tri(ethoxy)silane under mild conditions. The results showed that the homogeneous MnTPyP+ ions catalyzed the reaction where both branched and linear products were observed. Intercalation significantly enhanced both catalyst activity and selectivity. Production of the linear tri(ethoxy)silyl-1-octane as sole product was confirmed by FT-IR and NMR spectra, in the case of the intercalated catalyst. The activity enhancement was more pronounced in the case of the nano-particle supported catalyst system, with turnover frequency (TF) values up to 1200 min−1 and 85% conversion observed in less than 20 min. The intercalated catalyst systems were easy to recover and were reused three times, while retaining up to 80% of their original activity. Effects of different reaction parameters on the initial reaction rate, such as clay particle size, solvent polarity, reactant concentration, catalyst loading and temperature, were investigated. A new plausible mechanism, with evidence and justifications, is proposed.

Heterocycles from Nitrile Imines. Part III. Substituent Effect on Ring-Chain Tautomerism of 1,2,3,4-Tetrahydro-s-tetrazines

Selected series of 6-substituted 4-aryl-3-heteroaryl-1-methyl-1,2,3,4-tetrahydro-s-tetrazinea (V:1-12) were synthesized via direct interaction between appropriate nitrile imine and model methylhydrazonea. The extent of «ring-chain» tautomerism, as evidenced from nmr spectral data of V, is dependent on the nature of substituents at N-4, C-3, and C-6. The results reveal that: (i) The concentration of the cyclic tautomer tends to decrease as the basicity of the arylated N-4 decreases

Ring Transformation of Heterocycles: Part 3. A Conversion of 4-Amino-D2-1,2,4-oxadiazolines into 2-Arylamino-1,3,4-thiadiazoles and Oxaanalogues

4-Amino-Δ 2 -1,2,4-oxadiazolines (1) are transformed into the corresponding 2-arylamino-1,3,4-oxadiazoles (5) or thiadiazoles (6) via reaction with phenyl isocyanate (or phenyl isothiocyanate), followed by brief treatment of the resulting adducts (2 and 3) with trifluoroacetic anhydride at ambient temperature. Treatment of compounds (1) with trifluoroacetic anhydride gave 2-trifluoromethyl-1,3,4-oxadiazoles (8)

Arylamidoxime Complexes of Antimony(V)

Abstract Arylamidoximes (LH) react with SbCl5 to give adducts of the general formula SbCl5LH. Sodium arylamidoximates react with Ph3SbBr2 to give compounds of the general formula Ph3SbL2. These hexa-coordinated antimony complexes were characterized by elemental analyses, spectral data and conductivity measurements.

Heterocycles from Nitrike Oxides. Part V. 4-Amino-D2-1,2,4-oxadiazolines

Aryl nitrile oxides undergo 1,3-dipolar cycloaddition with alkanone hydrazones to give 4-amino-3-aryl-5,5-dialkyl-Δ 2 -1,2,4-oxadiazolines. Lead tetraacetate oxidation of these 4-amino-Δ 2 -1,2,4-oxadiazolines brings about smooth heteroring cracking into the corresponding nitrile, ketone, and nitrogen

Cyclopalladated Complexes of Arylamidoximes

Abstract Interactions of some arylamidoximes with lithium tetrachloro-palladate(II) in the presence of sodium acetate have been studied. The arylamidoximes investigated afford cyclopalladated, chlorobridged, binuclear complexes. The reaction of these complexes with triphenylphosphine is also examined. The products were identified on the basis of their elemental analysis, conductivity measurements, IR and NMR spectral data.

Ring transformation of heterocycles. II: Ring contraction of 5,6-dihydro-4H-1,2,4,5-oxatriazines into 1H-1,2,4-triazoles

6-Monosubstituted 5,6-dihydro-4H-1,2,4,5-oxatriazines (3) undergo ring contraction, via elimination of H 2 O, to yield the respective 1H-1,2,4-triazoles (4). This transformation is envisaged to proceed via the ring-opened (E)-hydrazonoxime (5) which then suffers dehydrative cyclization. The process is acid-catalyzed and is thermally induced. Apparently, the driving force for this transformation is linked to the aromaticity of the triazole product

Reactions of Ca, O-Dilithioximes with Functionalized Carbonyl Compounds. Part 1. Reaction with 1,2-Diketones

Cα.O-Dilithioximes add to symmetrical 1.2-diketones to give the 5.6-dihydroxy-1.2-oxazine derivatives. Under acidic conditions, the latter heterocycles undergo dehydration accompanied by ring contraction to 5-acyl-Δ 2 -isoxazolines

A study on the reaction of 3-alkyl(aryl)imidazo[1,5-a]pyridines with ninhydrin

Abstract The reaction of 3-alkyl(aryl)imidazo[1,5-a]pyridines (1) with ninhydrin in dichloromethane at room temperature delivered good yields of the respective 2-hydroxy-2-(imidazo[1,5-a]pyridine-1-yl)indene-1,3-diones. In the presence of dimethyl acetylenedicarboxylate (DMAD), this uncatalyzed electrophilic substitution reaction, involving C-1 (in 1) and the central C=O (in ninhydrin), takes precedence over the three-component 1,4-dipolar cycloaddition reaction. This selectivity is probably due to the higher electrophilicity of the carbonyl carbon-2 in ninhydrin as compared to that of the sp-carbon atoms in DMAD, augmented with the high nucleophilicity of carbon-1 in 1.