The main goal in this thesis has been to develop novel immobilization strategies leading to heterogenized catalysts with improved catalytic properties.
Firstly, a new family of polystyrene (PS)-supported cis-4-hydroxydiphenylprolinol derivatives has been prepared and evaluated in the tandem reaction between N-protected hydroxylamines and α,β-unsaturated aldehydes in batch and flow. The new immobilized catalysts compare favorably with previous, well-established catalysts, affording 5-hydroxyisoxazolidines as single diastereomers with high enantioselectivities and good yields.
Secondly, a PS-immobilized chiral isothiourea has been prepared and applied to the enantioselective acylative kinetic resolution of monoacylated BINOL(s) with inexpensive isobutyric anhydride in batch and flow. High selectivity and a remarkable stability of the catalytic system in the operation conditions have been recorded for unsubstituted BINOL. A continuous flow process has been implemented and operated with a 100 mmol (32.8 g) sample of racemic monoacetylated BINOL in a 84 hours experiment with a packed bed reactor containing 1 g (f = 0.37 mmol.g-1) of the functional resin.
Thirdly, we have used radical co-polymerization strategy to prepare a new family of PS-immobilized SPINOL-derived chiral phosphoric acids. The optimal immobilized species brings about the catalytic desymmetrization of 3,3-disubstituted oxetanes in excellent yields and enantioselectivities, exhibiting a very high recyclability. Finally, a continuous flow process has been implemented and operated for the sequential preparation of 17 diverse enantioenriched products.
In addition, the use of electricity as a green oxidant in combination with salts of abundant metals as catalysts has also been explored. We have thus developed a manganese/copper co-catalyzed electrochemical Wacker-Tsuji-type oxidation of aryl-substituted olefins, affording α-aryl ketones in moderate to excellent yields, with the advantages of avoidance of palladium as a catalyst and any external chemical oxidant, in an easily operated, cost-effective procedure.
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