Exploratory Investigations Probing a Preparatively Versatile, Pyridinium Salt Photoelectrocyclization-Solvolytic Aziridine Ring Opening Sequence

A novel pyridinium salt photoelectrocyclization-nucleophilic bicyclic aziridine ring opening reaction sequence has been investigated in order to determine its preparative potential. N-Alkylpyridinium perchlorates were found to undergo photoinduced electrocyclization upon irradiation in nucleophilic solvents, such as H(2)O and MeOH, to efficiently produce 6-alkyl-6-azabicyclo[3.1.0]hex-2-en-4-yl alcohols and ethers. The bicyclic aziridine photoproducts react with a number of different nucleophiles (e.g., H(2)O, MeOH, AcOH, AcSH) under acid-catalyzed conditions to produce 5-(nucleophile-substituted)-4-(alkylamino)cyclopenten-3-yl alcohols and ethers. The aziridine ring opening processes are both regioselective and stereoselective, yielding trans,trans-trisubstituted cyclopentenes exclusively, apparently as a consequence of the operation of an SN(2) mechanism. The effects of C-alkyl substitution on the regiochemistry of the pyridinium cation photocyclization reaction were briefly probed, and a method was developed to produce trans,cis-trisubstituted cyclopentenes by use of this tandem preparative sequence.     

Acceleration of Organic Reactions Using Microwave

The use of microwave technology in accelerating organic reactions has received intense attention leading to immense growth recently. Accordingly, we have been interested in improving the efficacy of organic processes by microwave irradiation. Here we report our results on the microwave assisted direct amide formation from carboxylic acid and amine, the hydrolysis of biopolymers, and nucleophilic aromatic substitution reaction. The reactions carried out under microwave irradiation, in general, …     

Facile cyclization of amidyl radicals generated from N-acyltriazenes

N-Acyltriazenes serve as a tin-free and initiator-free source for amidyl radicals. Thermal decomposition of N,N′-diaryl-N-(4-pentenoyl)triazenes in refluxing toluene led to the formation of monocyclic and tricyclic lactams in satisfactory yields via 5-exo amidyl radical cyclization.     

Solid Phase Synthesis of 4H-Pyrimido[2,1-b] Benzothiazol-4-ones from Resin-Bound Cyclic Malonic Ester

The solid phase synthesis of 4H-pyrimido[2,1-6] benzothizaol-4-ones has been reported.     

The molecular structure of norbornene as determined by electron diffraction and microwave spectroscopy

The molecular structure of norbornene has been investigated in the gas phase by combining electron diffraction data with microwave spectroscopic rotational constants. The interatomic distances (r_g) and bond angles were obtained by applying a least squares program to the refined experimental molecular diffraction intensities. The CC bond length was found to be 1.336 ± 0.002 Å while the

) bond length was 1. 529 ± 0.007 Å. Other bond lengths and angles included (IUPAC numbering system was used for norbornene): C₁-C₆ = 1.550 ± 0.020 Å, C₁-C₇ = 1.566± 0.005 Å, C₅-C₆ = 1.556 ± 0.005 Å, C-H_ave. = 1.103 ± 0.003 Å, ∠C₁C₂C₄ = 95.3°. The dihedral angle between planes C₁C₂C₃C₄ and C₁C₆C₅C₄ is 110.8 ± 1.5° while that between C₁C₂C₃C₄ and C₁C₇C₄ is 122.3°. The moments of inertia calculated from ED structure are in good agreement with microwave spectroscopic values.     

Molecular structure of 1,2,4-triazole

The molecular structure of 1,2,4-triazole has been determined by gas phase electron diffraction. The intemuclear distances and bond angles were obtained by applying a least-squares analysis to the experimental intensity. The bond distances (r_g) and bond angles were N₁-N₂ = 1.380 ± 0.010 Å, N₂C₃ = 1.329 ± 0.009 Å, C₃-N₄ = 1.348 ± 0.009 Å, N₁-C₅ = 1.377 ± 0.004 Å, N₄C₅ = 1.305 Å (calculated value). N-H = 0.990 Å, C-H = 1.054 Å, ∠N₁N₂C₃ = 102.7± 0.5°, ∠N₂C₃N₄ = 113.8 ± 1.3°, ∠N₂N₁C₅ = 108.9 ± 0.8°, ∠H₁N₁N₂ = 110.9°, ∠H₂C₃N₄ = 119.2°, ∠H₃C₅N₁ = 131.0°, ∠C₃N₄C₅ = 105.7° (calculated value) and ∠N₄C₅N₁ = 108.7° (calculated value).     

Total Synthesis of (+/-)-Leporin A

An efficient synthesis of (+/-)-leporin A (1) has been developed using a tandem Knoevenagel condensation-inverse electron demand intramolecular hetero Diels-Alder reaction to construct the key tricyclic intermediate 3 from pyridone 5 and dienal 6 in one pot in 35% yield. Hydroxylation (71%) of 3 and methylation (77%) of the resulting hydroxypyridone 2 completed the first total synthesis of (+/-)-leporin A (1).     

Study on osmotic pressures for aqueous lysozyme and alpha-chymotrypsin-electrolyte solutions with two Yukawa potentials

The equation of state (EOS) of Duh and Mier-y-Terán for one Yukawa potential is expanded to two Yukawa potentials to describe the nonidealities of the charged lysozyme and alpha-chymotrypsin solutions. Instead of the classical DLVO theory, the attractive dispersion and double-layer repulsion interactions are represented by two Yukawa potentials, respectively. For the aqueous lysozyme solutions, the only adjustable dispersion energy parameter epsilon/k is regressed and the average deviation is 1.76%. For the aqueous alpha-chymotrypsin solutions, two adjustable parameters (the molecular weight and dispersion energy parameter) are regressed and the average deviation is 7.62%. Some correlation and prediction results are discussed.     

Alcohol sensing membrane based on immobilized ruthenium(II) complex in carboxylated PVC and surface covalently bonded alcohol oxidase

Alcohol sensing membranes coated on overhead transparency films for the continuous monitoring of ethanol, propanol and butanol are presented. Alcohol oxidation catalyzed by alcohol oxidase in conjunction with the fluorescence quenching reaction of oxygen-sensitive dye ion-pair, tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) didodecylsulphate was chosen for the determination. Alcohol oxidase was immobilized covalently on a plasticized carboxylated poly(vinyl chloride) membrane and the oxygen-sensitive dye ion-pair was entrapped in the same membrane. The sensing membrane relates oxygen consumption, as a result of enzymatic oxidation, to alcohol concentration. Measurements have been performed in air-saturated alcohol standard solutions of pH 7.0. Storage stability, reproducibility and the effect of pH on sensing membrane performance have been studied in detail. The alcohol sensing membrane proposed here is simple to prepare and has a fairly rapid response time of <1 min. It has been successfully applied to the determination of the ethanol contents in various spirits.     

Synthesis of 2‐Dihydrooxadiazolinyl Chromones

Reactions of the substituted 2‐formyl chromones with aroylhydrazines gave corresponding 2‐(aroylhydrazonomethylidyne) chromones. Then 2‐(3′‐acetyl‐5′‐aryl‐2′,3′‐dihydro‐1′,3′,4′‐oxadiazol‐2′‐yl) chromones were prepared by these 2‐(aroylhydrazonomethylidyne) chromones under refluxing with Ac₂O. All target compounds were characterized through elemental analysis and IR, ¹H NMR, MS.