The crosslinked polymer microsphere-immobilized sulfonic acids and chiral prolinols were prepared by the precipitation polymerization of DVB, styrene, and monomer having sulfonic acid derivative 1 and prolinol moiety 2, respectively. (Scheme 1a and 1b). We examined polymeric acid-base catalysts' efficiency by applying in one-pot deacetalization-asymmetric Michael addition reaction (Scheme 1c). The first step involves the deacetalization of propionaldehyde diethyl acetal catalyzed by the sulfonic acid catalyst to produce propionaldehyde. The second step is the asymmetric Michael addition between the propionaldehyde as intermediate and methyl vinyl ketone (MVK) using polymeric chiral basic prolinol derivative. When the combination of p-toluenesulfonic acid and diphenylprolinol methyl ether catalysts was applied to the one-pot reaction, the reaction's overall yield was 81% with the racemic product. The overall yield was 9% by using p-toluenesulfonic and polymer microsphere-immobilized prolinol derivative Cat*S50. Even the linear polymer-immobilized sulfonic acid and Cat*S50 were used, the product was obtained in 75% yield with 18% ee. When both the acid and base catalysts were the polymer microsphere-immobilized catalyst, such as Cat*A and Cat*S50, good yield (82%) and excellent enantioselectivity (91%) of the product was found. The effect of molar ratio, catalyst loading, temperature, solvent, MVK & H2O amount, hydrophilicity, and hydrophobicity of prolinol derivatives were also investigated.

Design of polymer microsphere-immobilized chiral prolinol derivative: application in one-pot acid-base reaction by using site-isolation

ACS Spring Meeting 2021

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