Journal of Molecular Catalysis A-Chemical, Vol.182, No.1, 533-539, 2002
Homogeneous versus heterogeneous approach to the catalytic desymmetrisation of meso-anhydrides promoted by cinchona alkaloids
The ring opening of the cyclic prochiral cis-1,2,3,6-tetrahydrophthalic anhydride 1 with methanol was investigated by using cinchona alkaloids such as quinine (QN) and quinidine (QD) as base catalysts. The effect of solvent, temperature, reaction time and catalyst amount on the yield and enantio selectivity was examined in the model reaction under homogeneous conditions. The best results (yields and ee values) were achieved by using QD as chiral catalyst. Moreover, as a hypothetical intermediate, an adduct between the anhydride and the catalyst which is responsible for both reagents activation and stereocontrol is proposed. QD was then supported to both amorphous (KG-60) and mesoporous (MCM-41) siliceous materials through a thioether linker giving catalysts called KG-60-QD and MCM-41-QD, respectively. These materials were characterised by determining surface area, loading value and thermal stability. Comparison experiments showed that supported catalysts afforded product 3 in slightly lower yields and ee values with respect to the homogeneous counterpart. (C) 2002 Elsevier Science B.V. All rights reserved.
Keywords:cinchona alkaloids;asymmetric catalysis;meso-anhydrides;desymmetrisation;heterogeneous catalysis