A novel Sn(IV) aryloxide Lewisacid has been designed and prepared from SnCl4 and (S)-3,3′-bis(3,5-bis(trifluoromethyl)phenyl)-1,1′-bi-2-naphthol. The chiral Sn(IV) Lewisacid has been successfully applied to the enantioselective Diels–Alderreaction.
Enantioselective catalysts based on the chiral fragment (η5-C5Me5)Ir(Prophos) for Diels–Alder reactions
作者:Daniel Carmona、Fernando Viguri、Ainara Asenjo、Fernando J. Lahoz、Pilar García-Orduña、Luis A. Oro
DOI:10.1016/j.molcata.2014.01.021
日期:2014.4
The aqua complex (S-Ir,R-C)-[(eta(5)-C5Me5)Ir(Prophos)(H2O)][SbF6](2) [Prophos = (R)-propane-1,2-diyl-bis(diphenylphosphane)] is an active precursor for the asymmetric Diels-Alder reaction of acyclic enals with cyclopentadiene, 2,3-dimethylbutadiene and isoprene. Enantioselectivities up to 78% ee are achieved. The intermediate Lewis acid-dienophile complex (S-Ir,R-C)-[(eta(5)-C5Me5)Ir(Prophos)(ethyl acrolein)][SbF6](2) has been isolated and completely characterized, including the X-ray crystal structure determination. Structural parameters indicate that the disposition of the coordinated dienophile is controlled by CH/pi attractive interactions established between a phenyl group of the Prophos ligand and the aldehyde proton of the coordinated enal. Proton NMR data indicate that these interactions are maintained in solution. From diffractometric and spectroscopic data, the origin of the enantioselectivity is discussed. (C) 2014 Elsevier B.V. All rights reserved.
Reusable montmorillonite-entrapped organocatalyst for asymmetric Diels–Alder reaction
A chiral organocatalyst was successfully entrapped by montmorillonite clay using the cation-exchange method. The mont-entrapped organocatalyst acted as a highly efficient and reusable heterogeneous catalyst for the asymmetric Diels-Alder reaction, without loss of its initial activity. (C) 2008 Elsevier Ltd. All rights reserved.