Chitosan nanoreactor modified with PNIPAAm as efficient catalyst for preparation of chiral boron compounds in aqueous phase.

This work constructed chitosan-based core-shell catalytic nanoreactor (CS/NI/SA@Cu(II)) by free radical polymerization of biomass chitosan and temperature sensitive materials. The CS/NI/SA@Cu(II) were characterized by FT-IR, TG, XPS, SEM, TEM, and EDS to prove the formation of the nanoreactor, and the Cu content was obtained by ICP analysis. The TEM indicated that CS/NI/SA-2 presented a hollow core-shell structure with a size of about 100 nm, and the contact angle of CS/NI/SA-2 was 67°. The core-shell nanoreactors were successfully applied to the 1,4-chiral borylation reaction of α,β-unsaturated compounds, and α,β,γ,δ-unsaturated compounds, as well as the 1,6-chiral borylation reaction of methylene benzoquinone compounds in the aqueous phase. All template substrates can obtain up to 90 % yields with 90 % ee values in core-shell nanoreactors and chiral ligand in 12 h. The possible mechanism of catalytic reaction was revealed by calculation and deuteration experiment. Besides, the CS/NI/SA@Cu(II) could be easily recycled and effectively reused. Besides, the CS/NI/SA@Cu(II) could be easily recycled and effectively reused for 6 times. Remarkably, this approach provides the first report of biomass chitosan for an efficient strategy to gain chiral organic boron compounds in high yields and enantioselectivities.