Homogeneous versus heterogeneous approach to the catalytic desymmetrisation of meso-anhydrides promoted by cinchona alkaloids
✍ Scribed by Franca Bigi; Silvia Carloni; Raimondo Maggi; Alessandro Mazzacani; Giovanni Sartori; Giada Tanzi
- Book ID
- 104421803
- Publisher
- Elsevier Science
- Year
- 2002
- Tongue
- English
- Weight
- 101 KB
- Volume
- 182-183
- Category
- Article
- ISSN
- 1381-1169
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✦ Synopsis
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 enantioselectivity 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.