Polymeric cinchona alkaloids for the catalytic asymmetric dihydroxylation of olefins

Abstract

Three cinchona alkaloid copolymers (PMMA-BQTP, PMA-BQTP, PAN-BQTP) have been synthesized by copolymerization. Their structure was characterized by FTIR, GPC, and element analysis. The catalytic activity of these copolymers in asymmetric dihydroxylation (AD) of olefins by OsO 4 was studied. The products enantiomeric excesses (ee) and the conversion of the substrate in the dihydroxylation reactions were determined using HPLC. The effect of time, temperature, and recycle times on the reaction was also discussed. The results showed that the copolymers catalyzed the dihydroxylation of the olefins to get diols in high optical yield. However, their catalytic efficiency was largely depended on the nature of olefins. The polymeric cinchona alkaloid can be simply recovered at the end of the reaction by centrifugation and then reused without radical change of activity or enantioselectivity.

Simple Preparation of Dimeric Cinchona Alkaloid Derivatives on Polystyrene Supports and a Highly Enantioselective Catalytic Heterogeneous Dimerization of Ketenes

“…On the contrary, the access to IPB variants of the catalytically interesting dimeric ligands and catalysts 3 – 5 (Figure 1) has proved much less convenient. In fact, the immobilization of these non‐ionic, 9‐ O ‐heterocyclic ethers has been usually pursued by taking advantage of the 10,11‐double bond of the alkaloid moiety,8 either by direct radical addition of thiol groups supported onto siliceous materials,4a,5b,c or by intermediate conversion into anchorable derivatives (e.g., styryl or methacrylic monomers) 4a–c. However, both strategies appear less than ideal because of the low alkaloid loading and immobilization yield, in the case of the former, and the necessity of handling sensitive compounds, for the latter.…”

Recyclable Stereoselective Catalysts

“…The complex between osmium catalyst and 78 proved to have good recyclability. It maintained a consistent 80% yield for trans -stilbene dihydroxylation during six cycles, while the enantioselectivity decreased in the first two reutilizations from to 84% to a stable 65% ee …”

“…It maintained a consistent 80% yield for trans-stilbene dihydroxylation during six cycles, while the enantioselectivity decreased in the first two reutilizations from to 84% to a stable 65% ee. 183 Inorganic solid supports have been used for immobilization of cinchona ligands because they have some advantages over organic polymer-bound matrix. Besides having better me- chanical and thermal properties, they do not need to be carefully designed to perform AD reactions with high efficiency.…”

Synthetic methods : Part (ii) Oxidation and reduction methods

“…values, but activity varied for different substrates. 71 Two disclosures on Os-mediated dihydroxylation do not concern asymmetric induction. Lee and Lee have reported dihydroxylation catalysed by a polystyreneimidazolium resin-supported Os complex 72 and Fache has reported an unexpected and potentially synthetically useful simultaneous Os-mediated dihydroxylation/tosyl group removal.…”