On the chemistry of pyrrole pigments,LXXXVIII: Nonlinear optical properties of linear oligopyrroles

Summary The second order polarizabilities, _xxx, of six linear oligopyrroles of the arylalkylidene-dipyrrinone type (the synthesis of two of them is reported) were estimated from their solvatochromic shifts. A dimethylaminophenylmethylene and a benzodithioleylidenemethylene derivative (2,6) were found to exhibit rather high _xxx values.

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Zur Chemie von Pyrrolpigmenten, 88. Mitt.: Nicht-lineare optische Eigenschaften von linearen Oligopyrrolen

Zusammenfassung Die Polarisierbarkeiten zweiter Ordnung, _xxx, von sechs linearen Oligopyrrolen des Arylalkyliden-pyrrolinon-Typs (die Synthese zweier solcher Derivate wird mitgeteilt) wurden aus ihrem solvatochromen Verhalten abgeschätzt. Ein Dimethylaminophenylmethylen-und ein Benzodithiolylidenmethylen-Derivat (2,6) zeigen bemerkenswert hohe _xxx-Werte.

     

Direct organocatalytic asymmetric alpha-sulfenylation of activated C-H bonds in lactones, lactams, and beta-dicarbonyl compounds

The application of cinchona alkaloid derivatives as catalysts for enantioselective alpha-sulfenylation of activated C-H bonds in lactones, lactams, and beta-dicarbonyl compounds by different electrophilic sulfur reagents is presented. Optically active products are obtained in good to excellent yields and up to 91 % ee. Furthermore, the diastereoselective reduction of alpha-sulfenylated beta-keto esters to give optically active alpha-sulfenylated beta-hydroxy esters has been studied. A model for the intermediate is presented, in which the protonated cinchona alkaloid interacts with the substrate leading to face-shielding in accordance with the enantioselective alpha-sulfenylation step.     

Polymerization of isobutylene by the adamantane bromide–diethylaluminum chloride catalyst system

Isobutylene has been polymerized in a continuous stirred tank reactor using a catalyst system comprised of 1-bromoadamantane and diethylaluminum chloride. The polymerization was carried out in hexane solvent at ?15 to ?27°C and gave 100% conversion to polyisobutylene (PIB) of 1000–3000 M_w. The results of pyrolysis–gas chromatography–mass spectrometry analyses are consistent with a mechanism involving the formation of the adamantyl cabocation and its addition to an isobutylene molecule to initiate polymerization. ¹³C-NMR analyses show that the PIB products contain R₂C? CR₂ and R₂C? CHR olefin types. Information on the nature of these olefins and the route to their formation has been developed.     

Highly chemoselective hydrogenolysis of iodoarenes

The catalytic hydrodehalogenation reaction using molecular hydrogen and Pd/C has been revisited. It is shown that the speed of removal of halogen increases with increasing electronegativity I < Br < Cl. Nevertheless, selective dehydrohalogenation in compounds containing other reducible functions can be achieved only with iodine and not with bromine or chlorine. Selective deiodination of iodobenzophenone could be accomplished without reducing the carbonyl group. Hydrogenolysis of azidoiodoaromatic compounds to the corresponding azido compounds is high yielding. This selectivity was exploited for the labeling of benzophenone- and azido-containing compounds by deuterium and tritium.     

Antiprotozoal 6-substituted-5,6-dihydro-alpha-pyrones from Raimondia cf. monoica

Dichloromethane extracts of both the roots and the leaves of Raimondia cf. monoica showed in vitro antiplasmodial and leishmanicidal activities against Plasmodium falciparum and Leishmania panamensis, respectively. Three 6-substituted 5,6-dihydro-2H-pyran-2-ones were isolated. (1) and (2) were identified as (6S)-(5'-oxohepten-1'E,3'E-dienyl)-5,6-dihydro-2H-pyran-2-one (1) and (6R)-(5'-oxohepten-1'Z,3'E-dienyl)-5,6-dihydro-2H-pyran-2-one (2), respectively. (-)-Arentilactone (3) was also isolated. The structure of the new compound (1) was determined by spectroscopic methods; additional spectroscopic data for (2) are reported for the first time.     

Synthesis and characterization of new chiral palladium β-diimine complexes

The synthesis and characterization of a range of chiral β-diimine ligands and their complexes with palladium(II) has been investigated. The introduction of chirality can be easily achieved through a combination of both achiral and chiral building blocks. The absolute configuration of the stereochemical centers has been determined. In addition, representative X-ray structures of both ligands and complexes have been determined.