An efficient synthesis of cyercene A

An efficient approach to the total synthesis of the marine derived polypropionate cyercene A is described. A key feature of the synthesis is the development of methodology for the diastereoselective Wadsworth-Emmons type condensation of a functionalised γ-pyrone unit.     

A general method for the preparation of 4- and 6-azaindoles

Nitropyridines reacted with an excess of vinyl Grignard reagent to produce 4- or 6-azaindoles. Improved yields were obtained when a halogen atom was present at the position alpha to the nitrogen atom in the pyridine ring.     

An ab initio molecular orbital study of Li2O2 and LiO2H

An ab initio molecular orbital study, using a Gaussian basis set, of the geometries of Li₂O₂ and LiO₂H is presented. Consistent with the experimental data available, Li₂O₂ is found to have a rhombic structure; the O-Li-O configuration in LiO₂H is found to form an acute triangle. The bonding in these species is discussed to terms of Mulliken population analyses.     

Synthesis of an essentially alternating,aliphatic copolyamide

An essentially alternating copolyamide of 6-aminohexanoic acid and 11-aminoundecanoic acid was obtained by the condensation polymerization of methyl 11-(6-aminohexanamido)undecanoate. The monomer was synthesized by the following reaction steps: (1) nitration of cyclohexanone to α-nitrocyclohexanone; (2) cleavage of α-nitrocyclohexanone by methyl 11-aminoundecanoate to obtain methyl 11-(6-nitrohexanamido)undecanoate; (3) hydrogenation of the nitro group of the cleavage product. The polymer was characterized by its melting and crystallization behavior as determined by differential scanning calorimetry, by x-ray analysis, and by comparison with an equimolar, random copolyamide of the two amino acids.     

Semiclassical approach to collision-induced emission in the presence of intense laser radiation: An aspect in the study of cooperative chemical and optical pumping

Collion-induced emission in molecular systems in an intense laser field is studied using the semiclassical approach, with a view towards cooperative chemical and optical pumping in laser production. The formalism is developed with the electronic-field representation, which treats collision and radiative interaction on the same footing. Electronic-field surfaces can be regarded as forming spectra for spontaneous emission; and particular emission events can be accounted for by propagating classical trajectories on emission electronic-field surfaces. Pre-emission loss from the excited state is dealt with by propagating classical trajectories on a loss surface along a complex contour of emission branch points. This loss surface is derived on the basis of localized radiative couplings between electronic-field states and provides a framework to treat the general problem of discrete state-continuum interactions. The formalism is applied to a two-state, collinear exponential model to compute S-matrix elements and transition probabilities between asymptotic states.     

(RO)(2)Ta[tris(2-oxy-3,5-dimethylbenzyl)amine]: structure and lactide polymerization activities

The novel atrane-like six-coordinate (RO)(2)TaL complexes [where R = Me or Et and L = tris(2-oxy-3,5-dimethylbenzyl)amine] containing three six-membered rings have been synthesized and characterized. The R = Me complex is the first group 5 representative of this class of compounds structurally characterized by X-ray means. Somewhat surprisingly, these compounds failed to function as single-site initiators for the polymerization of l-LA to isotactic PLA and rac-LA to atactic PLA, whereas Ta(OEt)(5) and two titanium analogues ROTiL (where R = 2,6-di-i-PrC(6)H(3) and i-Pr) as well as Ti(O-i-Pr)(4) were effective catalysts for both polymerizations.     

Decarboxylative aldol reactions of allyl beta-keto esters via heterobimetallic catalysis

Mild and selective heterobimetallic-catalyzed decarboxylative aldol reactions involving allyl beta-keto esters have been developed. The reaction is promoted by Pd(0)- and Yb(III)-DIOP complexes at room temperature and involves the in situ formation of a ketone enolate from allyl beta-keto esters followed by addition of the enolate to aldehydes. The reaction is a new example of heterobimetallic catalysis in which the optimized reaction conditions require the addition of both metals.     

Superoxide-mediated dehydrohalogenation reactions of the pyrethroid permethrin and other chlorinated pesticides

Superoxide generated in DMF readily converts the dihalovinyl group of permethrin and related compounds to a haloethynyl moiety and yields major products from elimination reactions of DDT, $\text{cis}$-chlordane, and 1,2-dibromo-3-chloropropane (DBCP).     

Thermally resistant polymers containing the s-triazine ring

Aromatic dinitriles cyclize to form aromatic polymers containing the s-triazine ring. In this paper, these polymers are compared thermally with each other and with aromatic melamine polymers prepared via the aromatic diamine and cyanuric chloride. One perfluoroaromatic melamine polymer was prepared and compared with the other two types of polymers. The polymers (triazines and melamine) in which biphenyl was the backbone were increasingly stable up to 1000°C. in nitrogen. The triazine polymers as a group were the most stable. The perfluoroaromatic polymer was the most stable melamine up to 500°C. in air but was very unstable above 700°C.     

Capacity and uniform algebras

Let A be a uniform algebra on a compact space X, let M be the maximal ideal space of A, and consider an element ? of A. Choose a component W of $\text{C}$??(X). In 1963 Bishop showed that {$\text{y}\text{in}\text{M ¦ ?(y) ? W}$} can be made into a one-dimensional complex analytic space provided there is a subset G of W having positive area such that for each λ in $\text{G {y}\text{in}\text{M ¦ ?(y) = λ}}$ is finite. We show that the hypothesis of “positive area” may be replaced by “positive exterior capacity” and that no weaker condition will suffice.