Abstract
Homogeneous linear poly(tartrate ester) ligands provide high chemical yields and enantiomeric excesses in the epoxidation of trans-hex-2-en-1-ol using Ti(OPri)4-tert-butyl hydroperoxide. Branched poly(tartrate ester) can be use as heterogeneous ligands in the epoxidation of trans-hex-2-en-1-ol using Ti(OPri)4-tert-butyl hydroperoxide. Removal and recovery of the polymer catalyst is a simple filtration at the end of reactions.
Highlights
Immobilization of reactive species on a polymer support could provide many important advantages over analogous homogeneous systems; for example separation of the support from the reaction mixture can be achieved by simple filtration aiding isolation and purification procedures, reactive species can become more active and/or more selective due to changes in the microenvironment of the active sites, excess of a polymeric reagent can be readily employed without incurring a penalty in work-up, transition metal complexes and optically active catalysts might be efficiently retained for re-use, and noxious or toxic species might be encapsulated when bound to a macromolecule, with obvious advantages in environmental terms [1]
There are no reports of the successful immobilisation of the Sharpless Ti−tartrate ester-based asymmetric alkene epoxidation catalyst, despite this being a relatively long-standing and well used methodology
We started our studies to evaluate the possibility of mimicing the Sharpless procedure using these linear soluble optically active polymers as ligands to achieve efficient and enantioselective catalysis
Summary
Immobilization of reactive species on a polymer support could provide many important advantages over analogous homogeneous systems; for example separation of the support from the reaction mixture can be achieved by simple filtration aiding isolation and purification procedures, reactive species can become more active and/or more selective due to changes in the microenvironment of the active sites, excess of a polymeric reagent can be readily employed without incurring a penalty in work-up, transition metal complexes and optically active catalysts might be efficiently retained for re-use, and noxious or toxic species might be encapsulated when bound to a macromolecule, with obvious advantages in environmental terms [1]. Poly(tartrate ester)s 3a-3d were synthesized from L(+)-tartaric acid 1, diols 2 and 3 w-% p-toluene sulphonic acid as a catalyst using a standard polycondensation procedure, as shown in Scheme 1 [9]. The branched/crosslinked C8-alkyl group-containing poly(tartrate ester) gel 4 was synthesized from L-(+)tartaric acid 1 , 20 mol-% excess of 1,8-octanediol 2c and 3 w-% p-toluene sulphonic acid as a catalyst, as shown in Scheme 3 [9].
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