RESUMO
A new flavin catalyst 2 immobilized in an ionic liquid ([BMIm]PF6) was used for the highly selective oxidation of sulfides to sulfoxides by hydrogen peroxide. The sulfoxides were obtained in good to high yields and high selectivity without any detectable overoxidation to sulfone. The catalyst in the ionic liquid was recycled up to seven times without loss of activity or selectivity.
Assuntos
Flavinas/química , Líquidos Iônicos/química , Catálise , Peróxido de Hidrogênio , Estrutura Molecular , Oxirredução , Sulfetos/químicaRESUMO
Eight different flavin derivatives have been synthesized and the electronic effects of substituents in various positions on the flavin redox chemistry were investigated. The redox potentials of the flavins, determined by cyclic voltammetry, correlated with their efficiency as catalysts in the H2O2 oxidation of methyl p-tolyl sulfide. Introduction of electron-withdrawing groups increased the stability of the reduced catalyst precursor.
Assuntos
Flavinas/química , Alquilação , Catálise , Eletroquímica , Cinética , Modelos Moleculares , Conformação Molecular , Oxirredução , Sulfetos/químicaRESUMO
Small amounts of simple methoxy poly(ethylene glycol)s (MPEGs) have a beneficial effect on catalyzed asymmetric aryl and alkyl transfer reactions onto aldehydes. The enantiomeric excesses of the products are improved, and this "MPEG effect" allows a reduction of the catalyst loading by a factor of 10.
RESUMO
A new chiral MeO-PEG-supported ferrocenyl oxazoline was synthesized and successfully employed in the enantioselective phenyl transfer to aldehydes. The products were obtained in high yields and with excellent enantioselectivities (up to 97% ee). Furthermore, the recovery of the ferrocene was facile, and catalyst efficiency was maintained in subsequent reactions.
Assuntos
Benzaldeídos/química , Compostos Benzidrílicos/química , Compostos Ferrosos/síntese química , Oxazolona/análogos & derivados , Oxazolona/síntese química , Catálise , Compostos Ferrosos/química , Metalocenos , Polímeros/química , Estereoisomerismo , Zinco/químicaRESUMO
Addition and substitution reactions with carbon nucleophiles are fundamental processes in organic synthesis, and the development of general catalytic asymmetric variants thereof is still a major challenge today. In contrast to enantioselective alkyl transfer reactions, the corresponding arylations have not yet reached a high level of maturity. The existing protocols are either of no general applicability or are limited in terms of selectivity. This article summarizes established routes for catalytic asymmetric aryl transfer together with the latest developments in this area. The scope and limitations of this reaction are discussed.
RESUMO
A novel planar chiral cyrhetrene 1 has been identified as an efficient catalyst precursor for the asymmetric synthesis of diarylmethanol compounds 2 by phenylation of aldehydes. Compared to the corresponding ferrocene derivative, the performance of the cyrhetrene is superior or at least equally as good and gives excellent enantioselectivities even with catalyst loadings as low as 2 mol %.