Autoxidation antioxidants - the fight for forever.

Autoxidation limits the longevity of essentially all hydrocarbons and materials made therefrom - including us. The radical chain reaction responsible often leads to complex mixtures of hydroperoxides, alkyl peroxides, alcohols, carbonyls and carboxylic acids, which change the physical properties of the material - be it a lubricating oil or biological membrane. Autoxidation is inhibited by addtitives such as radical-trapping antioxidants, which intervene directly in the chain reaction.

Azo-dimethylaminopyridine-functionalized Ni(II)-porphyrin as a photoswitchable nucleophilic catalyst.

We present the synthesis and the photochemical and catalytic switching properties of an azopyridine as a photoswitchable ligand, covalently attached to a Ni(II)-porphyrin. Upon irradiation with 530 nm (green light), the azopyridine switches to the configuration and coordinates with the Ni ion. Light of 435 nm (violet) isomerizes the ligand back to the configuration, which decoordinates for steric reasons.

Pyridinyl Amide Ion Pairs as Lewis Base Organocatalysts.

Pyridinyl amide ion pairs carrying various electron-withdrawing substituents were synthesized with selected ammonium or phosphonium counterions. Compared to neutral pyridine-based organocatalysts, these new ion pair Lewis bases display superior catalytic reactivity in the reaction of isocyanates with alcohols and the -Morita-Baylis-Hillman reaction of hindered electrophiles. The high catalytic activity of ion pair catalysts appears to be due to their high Lewis basicities toward neutral electrophiles as quantified through quantum chemically calculated affinity data.

Mechanistic Analysis and Characterization of Intermediates in the Phosphane-Catalyzed Oligomerization of Isocyanates.

The mechanism of the oligomerization of aliphatic isocyanates catalyzed by trialkylphosphanes has been studied through low temperature P and N NMR spectroscopy combined with computational chemistry. A revised mechanism is proposed that contains several (spiro)cyclic pentacoordinate phosphorous intermediates. Previously reported spectroscopic data of a transient intermediate has been reevaluated and assigned to a cyclic intermediate containing a P-N bond by experiments with N-labeled isocyanate.

Highly diastereoselective preparation of aldol products using new functionalized allylic aluminum reagents.

Chloro-substituted triethylsilyl enol ethers derived from cyclohexanone and related ketones are converted with aluminum powder in the presence of indium trichloride to functionalized allylic aluminum reagents which represent a new type of synthetic equivalent of metal enolates. These allylic organometallics undergo highly diastereoselective additions to aldehydes and methyl aryl ketones, giving aldol products with a β-quaternary center.