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Relevant academic research and scientific papers

Multiple dendritic catalysts for asymmetric transfer hydrogenation

The first and second generation multiple dendritic ligands based on chiral diamine were synthesized in a convergent approach and were well-characterized by NMR and MS techniques. Their ruthenium complexes prepared in situ had good solubility in the reaction medium (azeotrope of formic acid and triethylamine) and demonstrated high catalytic activity and enantioselectivity comparable to monomeric catalysts in the asymmetric transfer hydrogenation of ketones and imines. Quantitative yields and for some cases a slightly higher enantioselectivity (up to 98.7% ee) were obtained in the dendritic catalysis. Considering the high local catalyst concentrations at the periphery, diones were tested for the possible synergic reactivity between catalytic units at the surface, while no apparent differences were noted.

Facile reduction of aromatic aldehydes, ketones, diketones and oxo aldehydes to alcohols by an aqueous TiCl3/NH3 system: Selectivity and scope

A simple and rapid procedure for the almost quantitative reduction of aromatic aldehydes, ketones, diketones and oxo aldehydes to alcohols by use of TiCl3/NH3 in aqueous methanol solution is reported. The reducing system distinguishes between different classes of aldehydes and/or ketones, and many functionalities that usually do not survive under reducing conditions are tolerated well. The concept of reversal of chemoselectivity has also been developed. A mechanism based on two sequential one-electron transfers from TiIII to the carbonyl carbon atom is proposed, the second SET becoming operative only in the presence of ammonium ion (either added or formed in situ). Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.

Design, synthesis and structure of new chiral squaric acid monoaminoalcohols and diaminoalcohols and their use as catalysts in asymmetric reduction of ketones and diketones

Many chiral squaric acid aminoalcohols and C2-symmetric diaminoalcohols have been synthesized and their in situ formed chiral boron heterocycles have been used as catalysts for the enantioselective reduction of prochiral ketones and diketones by borane to give alcohols with up to 99% enantiomeric excess and 99% yield. The effects of solvent, catalyst-substrate ratio and temperature were also investigated.

Studies toward Cyclic Trisulfides. Trisulfide Polymers and Sulfur Extrusion1

Attempts were directed toward the synthesis of a variety of cyclic trisulfides, particularly by the reaction of N,N'-dibenzimidazolyl sulfide with dithiols.Only one monomeric cyclic trisulfide was prepared by this method; other cases yielded either mixtures of oligomers characterized as low molecular weight (5000) polymers or as products which spontaneously extruded sulfur to give the cyclic disulfides.We conlude that only where osmometric molecular weights or X-ray structures have been determined are monomeric cyclic trisulfides unambiguously defined.