Enantioselective inductivity of optically active helical poly[3-(9-alkylfluoren-9-yl)propylene oxide]s in the addition of methyllithium to aldehydes

Optically active helical poly[( R or S )-3-(9-alkylfluoren-9-yl)propene oxide]s (poly-AFPOs) were used to induce the enantioselective addition of methyllithium to aldehydes. The addition of methyllithium to 4-methoxybenzaldehyde gave the highest enantioselectivity (88% ee) under the inducement of poly-AFPOs. Poly-AFPOs could be recovered simply by pouring the reaction mixture into methanol in the end of the reaction and separating the precipitated polymer via filtration. The recovered poly-AFPOs could be reused for many times to induce the enantioselective addition of methyllithium to aldehyde without losing their enantioselective inducement ability. The investigation of the optical rotation and the MALDI-ToF MS confirmed that, in the enantioselective addition induced by poly-AFPOs, the lithium cation was embedded in the hole of the helical column of poly-AFPOs, leaving the negative methyl ion outside the one-handed helical column. The methyl anion abutted tightly against the helical polymer and acquired a chiral environment. It was this helically chiral environment that resulted in the enantioselective inducement of the addition reaction.