摘要：The aryl-aryl linkage is found in a wide range of com- pounds, from natural products such as vancomycin and aporphine alkaloids to important unnatural compounds such as 1,1'-bi-2-naphthol and BINAP Although sev- eral procedures have been developed for the coupling of aryl moieties, many of them have limited applicability due to the harshness of functional group intolerance of the conditions required.
摘要：The wittig reaction of 1-[3,5-0-(1,1,3,3-tetraisopropyldisiloxane-1,3-diyl)-β-D-erythro-pentofuranos- 2-ulosyl]uracil (4) with Ph_3P=CHCO_2R (R=ethyl or tert-butyl) exclusively gave (Z)-2'-[(alkoxy- carbonyl)methylene] derivatives 5 and 13, respectively, in high yields. An unusual β-facial selectivity of thiophenol addition to the 2'-[(alkoxycarbonyl)methylene] moiety of 5 and 13 was observed, and this facial selectivity was found to be influenced by both the thiolate counter cation and the bulkiness of the alkoxy moiety.
摘要：The chemistry of dihydropyridines has attracted con- siderable research interest for decades. Dihydropy- ridines perform important biological function. For ex- ample, the reduced form of coenzyme β-nicotinamide adenine dinucleotide (NADH) bears the 1,4-dihydropy- ridine moiety.
摘要：The reaction of ketones (acetone, 1,1,1-trifluoropropan-2-one) with the oxidation sstem (arene- sulfonyl)imidazole (2)/H_2O_2/NaO_2/NaOH permits the in situ generation of the corresponing dimethyl- and methuyl(trifluromethyl)dioxirane in various solvents. Theis has been established by the chemoselective oxidation of azomethines 6, the diastereoselective oxidation of chloesterol (12), and ~18O-labeling experiments.
摘要：We have previously reported that the reaction of dimethyl (Z)-2-butenylene dicarbonate (1) with acetylac- etone (2a) or methyl acetylacetate (2b)in the presence of a palladium catalyst coordinated with a chiral ferro- cenylbisphosphine or ruthenocenylbisphosphine ligand forms optically active vinyldihydrofuran 3 in up to 86/100 ee~1,2 (Scheme 1).
摘要：A series of 2-diazo-N-(3,4-dimethoxyphenyl)ethyl]-N-hept-6-enolymalonamidews were prepared and treated with a catalytic amount of rhodium(II) perfluorobutyrate. The resultant carbenoids undergo facile cyclization onto the neighboring amide carbonyl oxygen atom to generate isomunch- none-type intermediates. Subsequent 1,3-dipolar cycloaddition across the pendant olefin affords intramolecular cycloadducts in high yield.
摘要：A range of π-electron-rich macrocyclic polyetehrs incorporating dioxybnzene (hydroquinone) and/ or dixynaphthalene units have been synthesized in good yields by simple two-step procedures. Thehse macrocycles are able to bind bipyridinium-based guests as a result of a series iof cooperative Noncovalent bonding interactions. These molecular recognition events can be extended to the self- Assemb ly of catenanes incorporating the bipyridinium-based cyclophane, cyclobis(paraquat-p- Phenylene), and the macrosyclic polyethers incorporating dioxybenzene and -naphthalene unites.
摘要：Reviews are listed in order of appearance in the sources indicated. In multidisciplinary review journals, only those reviews which afll within the scope of this Journal are included. Sources are listed alphabetically in three categories: regularly issued review jornals and series volumes, contributed volumes, and other monographs. Titles are numbered serially, and these numbers are used for reference in the index.
摘要：A structurally and electronically divers set of anisoles are dihapto-coordinated to the π-base pentaammineosmium (II) and treated with a variety of carbon electrophiles (e.g. Michael acceptors, acetals). After deprotonation of a 4H-anisolium intermediate with a tertiary amine base, C(4)- substituted anisole complexes are isolated. The functionalized arenes are removed from the metal center either b y mild heating or treatment with an oxidant (e.g. AgOTf, DDQ, CAN).
摘要：The title reactions are subjected to a kinetic study in water, 25.0 deg C, ionic strength 0.2 M (MCI). Under amine excess, pseudo-first-order rate coefficients are found, which are linearly related to The free amine concentration. No dependence of the slopes of these plots (k_N) on the pH values Was observed. The Bronsted-type plots (log K_N vs PK_a of te pyridines) are biphasic with slopes β_1 =0.2 (high pK_a) for both reaction series and β_2=1.0 and 0.9 (low Pk_a) for the dinitro and the trinitro derivatives, respectively, and with the curvature centre at pK_a=pK_a 0=6.9 and 5.6 for the dinitro and the trinitro compounds, respectively.
摘要：In the presence of iodotrimethylsilane (TMSI) and lithium iodide in tetrahydrofuran, the otherwise unreactive copper acetylides add to enones present as s-trans conformers to provide good yields of the silyl enol ethers of β-acetylido carbonyl compounds. Typically good substrates are 2-cyclopen- tenone, 2-cyclohexenone, α,β-unsaturated aldehydes, and β-alkoxy-α-enones.
摘要：γ-Trifluoromethylated propargylic alcohols have been obtained in optically pure forms via effective enzymatic kinetic resolution and then converted into (E)- or (Z)-aloylic alcohols. [2,3]-Wittig rearrangement of the corresponding [[γ-(trifluoromethyl)allyl]oxy]acetic acid methyl esters afforded α-hydroxy-β-(trifluoromethyl)-γ,δ-unsaturated carboxylic acid methyl esters in good yields.
摘要：Ab initio MO study (at the ROHF,GVB, and CASSCF levels) of m-phenylenediamine (1) and 2,4- diamino-1,3,5-triazine (2) dication diradicals, which are model molecules of two possible high-spin polyers, poly(m-aniline) and poly(imino-1,3,5-triazinediyl) cation radicals, is presented. On the basis of qualitative MO considerations, it was seen that the electronic structures of 1~2+ and 2~2+ differed considerably.
摘要：In spite of the numerous synthetic poathways repoorted for the preparation of azacrown macrocycles, they are still relatively unavailable because of their high cost and the tedious and many-step procedures for their syntheses and isolation. A recently reported synthesis gave cyclen (1,4,7,10-tetraazacyclododecane) in a two-step process in a yield of 57/100~2.
摘要：A total synthesis of the isoprostane (±)-8epi-PGF_2α ethyl ester (5) is described, based on the diastereoselective cyclization of α-diazo ketone 7. This ketone is assembled by aldol condensation between α-diazo ketone 8 and aldehyde 9. The sequential α-diazo ketone aldol/insertion described here offeres a powerful new approach to cycloalkane construction.
摘要：The rates of thermolysis of α,α-difluoro β-lactones 1, leading to CO_2 and 1,1-difluoro olefins, have been obtained in the gas phase and in solution, and the activation parameters are reported. Ab initio calculations on the fluoro and nonfluorinated β-lactone systems are also reported. The gas- phase kinetic and theoretical results are discussed in terms of a probable concerted, asynchronous, nonpolar mechanism, whereas the solution kinetics, which include extensive solvent effect studies, are discussed in terms of a polar mechanism which probably involves formation of a zwitterionic intermediate.
摘要：β-Lactones (2-oxetanones) have recently emerged as important synthetic targets due to their occurrence in a variety of natural products, their utility as versatile synthetic intermediates, and their use as monomers for the preparation of biodegradable polymers.
摘要：Several investigations of rigid α-keto cyclopropane cleavage by O-stannyl ketyls are summarized herein. Tricyclo[188.8.131.52~2,8]octan-3-one ring systems were treated with nBu_3UnH, which produced different ring-cleavage products depending on the location and type of substitutnt present. An examination of both radical-ctabilizing substituents and stereoelectronic factors was initiated to understand what factors bias bond cleavage in a configurationally restricted α-ketocyclopropane via O-stannyl ketyls.
摘要：Reaction of 2-aryl-1,3-dioxane with arenes in the presence of a catalytic amount of trifluoromethane- sulfonic acid gave the corresponding diarylmethanes in good to excellent yields. The acid-catalyzed Friedel-Crafts benzylation of arenes could altenatively be carried out using arenecarbaldehyde And 1,3-propanediol. The reaction was assumed to proceed through a redox process involving Hydride shift from the cyclic acetal moiety to the benzylic carbon.
摘要：The complexes of 12-crown-4 (12C4), cyclen (12N4), and 1,4,7,10-tetrathiacyclododecane (12S4) with γ-cyclodextrin (γ-CD) were studied by NMR diffusion measurements in the absence and in the presence of inorganic and organic salts. The 12-crown-4:γ-CD system was also used to evaluate the effect of the nature of the cation and the anion on the association between the macrocycle and the γ-CD. In addition, we have studied the solvent effect and the pH effect on the association constant of the γ-CD:12C4 complex.