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Catalytic hypervalent iodine(III) mediated halogenations and oxidative dearomatisation cascades
thesisposted on 15.02.2017, 04:50 by Ngatimin, Marsewi
In recent years, the use of hypervalent iodine(III) reagents in organic synthesis has gained popularity due to their similar reactivities to those of toxic heavy metal reagents. Additional advantages, which render them more synthetically useful, are their high selectivity, ready availability and easy handling. Although a range of transformations has been achieved with these reagents, several areas remain under-developed, providing opportunities to contribute to this emerging field. One such area with limitations is halogenations. Since halogenated compounds are among the most versatile in organic synthesis, the development of mild and effective reagent system is of great practical value. The development of a versatile hypervalent I(III) reagent-mediated α-chlorination of α, β-unsaturated carbonyls, and dihalogination of simple alkenes, is presented in Chapter Two of this thesis. An enantioselective variant of the dihalogenation reaction was also explored with a chiral hypervalent iodine reagent. Another under-developed area is the oxidative cyclisation of electron rich aromatics to generate complex polycycles. The development of an oxidative cyclisation employing non-traditional nucleophiles, in particular electron rich vinylogous esters is detailed in Chapter Three of this thesis. The related catalytic reaction cascade utilising an electron rich ketone, together with a second nucleophile on the vinylogous ester is presented in Chapter Five of this thesis. Finally, although catalytic enantioselective utilisation of hypervalent I(III) reagents has been achieved, there is much room, and great need for further development. Significant contributions to this area were achieved by developing catalytic variants of our oxidative cyclisation of electron rich vinylogous ester and its related reaction cascade. In addition, a new chiral aryl iodide was synthesised and utilised in the oxidative cyclisation reaction, and is detailed in Chapter Four. Although the chiral aryl iodide promoted the reaction, no significant enantioselectivity was observed.