Recyclable Chiral Bifunctional Thioureas Derived from [60]Fullerene and Their Use as Highly Efficient Organocatalysts for the Asymmetric Nitro-Michael Reaction

Producción CientíficaThree novel fullerothioureas derived from natural valine, phenylalanine, and tert-leucine have been prepared by Prato's reaction of [60]fullerene and the corresponding aldehydes. These hybrids have been used as organocatalysts in a typical stereoselective nitro-Michael addition reaction under homogeneous and neat conditions. The catalysts are easily recoverable by filtration, and are recyclable for at least five times. The addition products were obtained in excellent yields and stereoselectivities by using catalyst loadings of as low as 0.5 mol-%.2018-07-07Ministerio de Economía, Industria y Competitividad (Project CTQ2014-59870-P

Advances in Organic and Organic-Inorganic Hybrid Polymeric Supports for Catalytic Applications

In this review, the most recent advances (2014–2016) on the synthesis of new polymer-supported catalysts are reported, focusing the attention on the synthetic strategies developed for their preparation. The polymer-supported catalysts examined will be organic-based polymers and organic-inorganic hybrids and will include, among others, polystyrenes, poly-ionic liquids, chiral ionic polymers, dendrimers, carbon nanotubes, as well as silica and halloysite-based catalysts. Selected examples will show the synthesis and application in the field of organocatalysis and metal-based catalysis both for non-asymmetric and asymmetric transformations

Recyclable Heterogeneous and Low-Loading Homogeneous Chiral Imidazolidinone Catalysts for alpha-Alkylation of Aldehydes

Two polystyrene-supported and six homogeneous MacMillan imidazolidinone catalysts were prepared and tested for the asymmetric a-alkylation of propanal with benzodithiolylium tetrafluoroborate. The chiral imidazolidinone was linked to polystyrene through the N-3 atom or through the phenyl ring and their catalytic activity was compared with that of their unsupported precursors. This comparison has allowed us to find an unsupported catalyst that displays high catalytic activity down to 5 or 2 mol% at room temperature with a high level of enantioselectivity also when used with hexanal and 3-phenylpropanal. In addition, one of the heterogeneous materials was revealed to be highly recyclable for at least eight cycles with no loss in efficiency working at the same levels of activity and enantioselectivity as the unsupported counterpart

A Simple Procedure for Oxidation of Alcohols using [Bis(acetoxy)iodo]benzene and a Catalytic Amount of Bromide Ions in Ethyl Acetate

primary and secondary benzylic alcohols and secondary aliphatic alcohols were oxidized to the corresponding aldehydes and ketones using [bis(acetoxy)iodo]benzene (BAIB) and a catalytic amount of bromide ions, from tetrabutylammonium bromide or KBr, in ethyl acetate. The catalytic role of bromide ions was also highlighted in the oxidation of primary aliphatic alcohols and secondary allylic alcohols carried out in the presence of 1 mol% of TEMPO