Asymmetric Inductivity Of Helical Poly(alkylfluorenylpropene Oxides) In The Addition Of Methyllithium To Aldehydes

Recently, in our group, a series of optically active helical poly[(R or S)-3-(9-alkylfluoren-9-yl)propene oxide] s (polyethers) had been synthesized via polymerization of optically active epoxides with bulky rigid group (9-alkylfluoren-9-yl) using KOH as an initiator and showed a stable helical conformation in solution via characterization by optical rotation and CD spectrum.Yashima et al first reported that functional poly(phenylisocyanide)s with a macromolecular helicity memory enantioselectively catalyzed a direct aldol reaction. Poly(phenylisocyanide)s had no other chiral factors except itself single-handed helicity. The catalyzed reaction showed enantioselective (ee:8-12%).We explored enantioselective inductivity of the optically active polyethers in the addition of alkai-metal reagents (methyllithium, ethynyl sodium, potassium cyanide) to aldehydes. Only the addition of methyllithium to aldehydes showed enantioselective. Then, we discussed the enantioselective inductivity of optically active polyethers in the addition of methyllithium to aldehydes, including the reaction condition optimization and substrates expansion. After optimizing, the addition of4-methoxybenzaldehyde with methyllithium had the highest enantioselectivity under the inducement of polyethers and the highest ee was88%. Polyethers could be recovered simply by pouring the reaction mixture into methanol after the reaction finished and separating the precipitated polymers via filtration. The recovered polyethers could be reused for many times to induce the enantioselective addition of aldehydes with methyllithium without losing their inducement ability. The investigation of the optical rotation, the MALDI-ToF MS and the inducement of polymer repeat unit confirmed that, in the enantioselective addition induced by polyethers, the lithium cation was embedded in the hole of helical column of the polyethers, leaving the negative methyl ion outside the one-handed helical column. The methyl anion abutted tightly against the helical polyethers and acquired a chiral environment. It was this helically chiral environment that resulted in the enantioselective inducement of the addition reaction.