A molecular orbital study of trans-polyenes to 18 double bonds

Calculations involving molecular orbitals have appeared in the chemical literature over the past few years, but all have used smalltrans-polyenes. We now report extended Huckel molecular orbital calculations ontrans-polyenes of up to 18 double bonds (36 carbons and 38 hydrogen atoms). Information obtained from these calculations include total energies, bond gaps, and net charges on each atom. Also found is that the band gap approaches 1.41 eV as the number of double bonds approaches infinity. This value is quite close to reported experimental values. Data are also presented for polyenes assuming equal C-C bond lengths.     

Isolation,identification and synthesis of the sex pheromone of the citrus mealybug,Planococcus citri (risso)

The sex attractant pheromone of the citrus mealybug, $\text{Planococcus citri}$ (Risso), has been Identified as (1$\text{R}$-$\text{cis}$)-(+)-2,2-dimethyl-3-(1-methylethenyl)cyclobutanemethanol acetate (VI).     

Functionalized organosilica microspheres via a novel emulsion-based route

Thiol-functionalized organosilica microspheres were synthesized via a two-step process: (1) acid-catalyzed hydrolysis and condensation of 3-mercaptopropyltrimethoxysilane (MPTMS), followed by (2) base-catalyzed condensation, which led to the rapid formation of emulsion droplets with a narrow size distribution. These droplets continued to condense to form solid microspheres. Solution (29)Si NMR and optical microscopy were applied to study the mechanism of this novel synthetic route. Solid-state (29)Si NMR, SEM, zeta potential titration, and Coulter counter measurements were used to study the bulk and surface properties and to determine the particle size distributions of the final microspheres. Compared to conventional St?ber silica particles, these microspheres were shown to have a lower degree of cross-linking (average degree of condensation, r = 1.25), a larger average size (up to 6 microm), and a higher isoelectric point (pH = 4.4). Confocal microscopy of dye-labeled microspheres showed an even distribution of dye molecules throughout the interior, characteristic of a readily accessible and permeable organosilica network. These findings have implications for the production of functionalized solid supports for use in catalysis and biological applications, such as optically encoded carriers for combinatorial synthesis.     

Cluster Build-up Reactions using Di-gold Cationic Fragments: Synthesis and Structural Characterization of [Os7(CO)19(Au2dppm)]

The reaction of the di-gold cation [Au₂(dppx)]²⁺ with the heptanuclear cluster dianion [Os₇(CO)₂₀]^2– affords the mixed metal cluster [Os₇(CO)₂₀{Au₂(dppx)}] (x=m (1), e (2), b (3)). On standing, in solution, this complex undergoes decarbonylation to give the cluster [Os₇(CO)₁₉{Au₂(dppx)}] (x=m (4), e (5), b (6)). The complexes have been characterised spectroscopically, and an X-ray structure determination of the dppm derivative shows that it contains a metal core based on an Os₇ edge-bridged bicapped tetrahedron with the two ₃-Au atoms capping adjacent triangular Os₃ faces of the central tetrahedron. In an analogous reaction, the carbido anion [Os₇(H)C(CO)₁₉]^– affords the neutral cluster [Os₇C(CO)₁₉{Au₂(dppm)}] (7) when treated with [Au₂(dppm)]²⁺ in the presence of base.     

Synthesis and reactions of 4-isopropylidene-1-aryl-3-methyl-2-pyrazolin-5-ones

The reactions of 4-isopropylidene-1-aryl-3-methyl-2-pyrazolin-5-ones 4a-d were investigated under a variety of conditions. In the presence of thiols or piperidine, 4a-d failed to yield conjugate addition products, presumably due to the steric bulk provided by the two methyl substituents of the isopropylidene side chain. Reaction of 4a-d with hydrazine derivatives gave the 1-aryl-3-methyl-2-pyrazolin-5-ones 3a-d and isopropyl-hydrazones. Treatment of 4a with potassium cyanide yielded a stable conjugate addition product which exists as a mixture of tautomers in different solvents. Also, oxidation of 4a with hydrogen peroxide gave a spiroepoxide 22 , while m-chloroperbenzoic acid oxidation afforded both the spiroepoxide 22 , and a small quantity of a hydroxyspiroepoxide 23.     

Rearrangement of spiro-benzimidazolines: preparation of N-alkenyl- and N-alkyl-benzimidazol-2-ones

A synthetically useful protocol has been developed for the preparation of highly functionalized N-alkenyl-benzimidazol-2-ones. Reaction of commercially available o-phenylenediamines with variously substituted cyclic ketones provides spiro-benzimidazolines. Treatment of these spiro-benzimidazolines with triphosgene in the presence of potassium carbonate results in rapid rearrangement and formation of N-alkenyl-benzimidazol-2-ones in modest to excellent yield for the two-step sequence. Extension of this methodology toward the preparation of a μ opiate receptor antagonist and droperidol, a potent antiemetic and antipsychotic agent, currently a marketed pharmaceutical is also described. Upon treatment of spiro-benzimidazolines with triphosgene in the presence of sodium triacetoxyborohydride, N-alkyl-benzimidazol-2-ones were formed.     

Synthesis and Characterisation of a Thiocarbonyl containing Osmium Cluster

Reaction of CS₂ with H₂Os₃(CO)₈(MeCN)S in cyclohexane yields a product H₂Os₃(CO)₇(CS)S₂. this has been characterised by NMR and mass spectroscopy, and by X-ray analysis, and has been shown to contain a terminal thiocarbonyl ligand.     

Enantioselective Preparation of 2‐Aminomethyl Carboxylic Acid Derivatives: Solving the β2‐Amino Acid Problem with the Chiral Auxiliary 4‐Isopropyl‐5,5‐diphenyloxazolidin‐2‐one (DIOZ). Preliminary Communication

Multigram amounts of suitably protected β²‐amino acids with 17 of the 20 proteinogenic side chains are prepared by diastereoselective reactions of Li, B, or Ti enolates of the corresponding 3‐acyl‐4‐isopropyl‐5,5‐diphenyloxazolidin‐2‐ones (acyl‐DIOZ; 1 ) with appropriate electrophiles (amidomethylation, hydroxyalkylation, (benzyloxycarbonyl)methylation) in yields of 55–90% and with diastereoselectivities of 80 to >97% (Scheme). The primary products 2 – 8 thus obtained are converted to protected β²‐amino acids by standard procedures (Table 1). Many of the DIOZ derivatives are highly crystalline compounds (31 X‐ray crystal structures in Table 2). The chiral auxiliary DIOZ, readily prepared in either enantiomeric form, is recovered with high yield.     

Gas chromatographic optimization studies on the side chain and ring regioisomers of methylenedioxymethamphetamine

Gas chromatographic (GC) optimization studies are conducted for the 10 methylenedioxyphenethylamine regioisomeric substances related to the drug of abuse 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy). These 10 compounds, having the same molecular weight and equivalent major mass spectral fragments, are not completely resolved using typical GC-mass spectrometry screening methods for illicit drugs. MDMA coelutes with at least one nondrug regioisomer under standard drug screening conditions. Separation of the 10 regioisomers is studied using stationary phases of varying polarities. Resolution optimization shows that very slow program rates give the best separation for the nonpolar stationary phases, requiring analysis times of as much as 85 min. Narrow-bore columns containing the same nonpolar stationary phases improve the analysis time to approximately 29 min. The polar stationary phase DB-35MS allows high-temperature programming rates, yielding complete resolution of all 10 compounds in less than 7 min. Temperature program optimization studies on the DB-35MS phase allow the separation time to be reduced to approximately 4.5 min.     

The identification of 10 and 11 substituted 7H-benzimidazo[2,1-a]benz[de]isoquinolin-7-ones through 1N NOE studies on their methyl p-toluenesulfonate salts

The spectral similarities of 10 and 11 substituted 7H-benzimidazo[2,1-a]benz[de]isoquinolin-7-ones hinder the identification of the individual isomers. Preparation of the 13-methyl p-toluenesulfonate salts of these compounds has allowed the assignment by the use of NOE techniques. Saturation of the N-methyl caused an NOE at H-12. The coupling pattern of H-12 then provides identification of the compound.