Synthesis of 1,3-difluoroaromatics in one pot by addition of difluorocarbene from sodium chlorodifluoroacetate to 1,2-substituted cyclobutenes

[formula: see text] The synthesis of 1,3-difluoro-2,4-diphenylbenzene has been accomplished in one step from 1,2-diphenylcyclobutene using the environmentally benign difluorocarbene precursor sodium chlorodifluoroacetate. In addition, the preparation of the previously unknown compound 1,3-difluoro-2,4-di-n-propylbenzene has been accomplished in one step from 1,2-di-n-propylcyclobutene using Seyferth's reagent (Ph-Hg-CF3) and sodium chlorodifluoroacetate.     

Reinvestigation of mucohalic acids,versatile and useful building blocks for highly functionalized alpha,beta-unsaturated gamma-butyrolactones

[reaction: see text] Mucohalic acids (mucochloric acid (1, 3,4-dichloro-5-hydroxy-5H-furan-2-one) and mucobromic acid (2, 3,4-dibromo-5-hydroxy-5H-furan-2-one)) are inexpensive, commercially available starting materials with multiple functional groups. These compounds have been modified by way of reduction followed by Suzuki cross-coupling reactions involving arylboronic acids to afford highly functionalized alpha,beta-unsaturated gamma-butyrolactones in excellent yield. The synthetic utility of these building blocks was effectively demonstrated through preparation of the antiinflammatory drug Vioxx.     

Toward a stable apoptolidin derivative: identification of isoapoptolidin and selective deglycosylation of apoptolidin

[formula: see text] Isoapoptolidin was isolated from crude fermentation extracts of the apoptolidin-producing microorganism Nocardiopsis sp. Apoptolidin isomerizes to isoapoptolidin upon treatment with methanolic triethylamine to establish a 1.4:1 equilibrium mixture of isoapoptolidin and apoptolidin. Semisynthesis of a peracetylated and deglycosylated derivative of apoptolidin is also described.     

High-throughput approaches for the discovery and optimization of new olefin polymerization catalysts

The discovery of new olefin polymerization catalysts is currently a time-intensive trial-and-error process with no guarantee of success. A fully integrated high-throughput screening workflow for the discovery of new catalysts for polyolefin production has been implemented at Symyx Technologies. The workflow includes the design of the metal-ligand libraries using custom-made computer software, automated delivery of metal precursors and ligands into the reactors using a liquid-handling robot, and a rapid primary screen that serves to assess the potential of each metalligand-activator combination as an olefin polymerization catalyst. "Hits" from the primary screen are subjected to secondary screens using a 48-cell parallel polymerization reactor. Individual polymerization reactions are monitored in real time under conditions that provide meaningful information about the performance capabilities of each catalyst. Rapid polymer characterization techniques support the primary and secondary screens. We have discovered many new and interesting catalyst classes using this technology.     

Understanding conditions for which biological effects of nonionizing electromagnetic fields can be expected

Scientific interest in the interaction of nonionizing electromagnetic fields with biological systems is longstanding, but often still controversial. Theories, models and computer simulations have usually emphasized physical interactions with subsystems (e.g. cell membranes) of a biological system. By extending this first necessary physical step to a second step of explicitly and quantitatively considering chemical changes, increased understanding appears possible. In the case of "strong fields", the role of field-altered chemistry is important to electrochemotherapy [Biochem. Pharmacol. 42, Suppl. (1991) 567] and creation of transdermal microconduits [Bioelectrochem. Bioenerg. 49 (1999) 11; J. Controlled Release 61 (1999) 185; J. Invest. Dermatol. 116 (2001) 40] For "weak fields" (a topic with much more controversy) consideration of chemical change shows that organized multicellular systems can be understood to respond to extremely small electric [Chaos 8 (1998) 576] or magnetic fields [Nature 405 (2000) 707]. In contrast, isolated individual cells interacting via voltage-gated channels [Proc. Natl. Acad. Sci. 92 (1995) 3740; Biophys. J. 75 (1998) 2251; Bioelectromagnetics 20 (1999) 102], or processes without "temperature compensation" [Biophys. J. 76 (1999) 3026], appear implausible. Satisfactory understanding is likely only if experimental and theoretical work is reconciled, which should therefore be emphasized. The interaction of electromagnetic fields with biological systems is of interest because of fundamental scientific curiosity, potential medical benefits and possible human health hazards.     

CO(2) capture by a task-specific ionic liquid

Reaction of 1-butyl imidazole with 3-bromopropylamine hydrobromide, followed by workup and anion exchange, yields a new room temperature ionic liquid incorporating a cation with an appended amine group. The new ionic liquid reacts reversibly with CO2, reversibly sequestering the gas as a carbamate salt. The new ionic liquid, which can be repeatedly recycled in this role, is comparable in efficiency for CO2 capture to commercial amine sequestering reagents, and yet is nonvolatile and does not require water to function.     

Synthesis and spectroscopic properties of elongated ruthenium dihydrogen complexes: temperature and isotope dependence of H-H distances

Several dihydrogen complexes of ruthenium of the form [Cp/Cp*Ru(P-P)H(2)](+) (P-P = chelating diphosphine ligand) have been prepared by reaction of the corresponding neutral chloride complexes with H(2) in the presence of NaB(ArF)(4). Treatment with D(2) or T(2) gas leads to incorporation of deuterium or tritium in the dihydrogen ligand. Measurement of the resulting H-D and H-T couplings as a function of the temperature and magnetic field gives results consistent with computational studies which predict that the H-H bond distance will increase with temperature and will be significantly shortened by isotopic substitution. The degree of the observed temperature dependence is found to be a critical function of the ancillary ligand set.