| Summary: | Reduction of N-heteroaromatic compounds is a challenging and important reaction. Transfer hydrogenation using organic molecules as hydrogen donors is a safe and operationally simple alternative to hydrogenation with H2. However, it has been underutilised and less developed. In this thesis, our contribution to the transfer hydrogenation of N-heteroaromatic compounds is described. Following a brief introduction of transfer hydrogenation of N-heteroaromatic compounds in Chapter 1, Chapter 2 presents a novel method for the mild reduction of quinolines, isoquinolines and quinoxalines to corresponding tetrahydro products. The most significant discovery is the remarkable accelerating effect of the simple iodide ion, which acts presumably by altering the reaction mechanism. Chapter 3 extends the above-mentioned system to the reduction of more challenging pyridines to afford not only piperidines but also the 3,4-unsaturated variants with high chemoselectivities. Chapter 4 describes a simple, complementary system, discovered during searching for new transfer hydrogenation catalysts, which allows for the hydrogenation of N-heteroaromatics with H2 using a cyclometalated iridium complex under exceptionally mild conditions (ambient temperature, 1 atm H2) in the absence of any additives. Chapter 5 demonstrates a new reaction for the rapid and direct preparation of various chiral piperidines from pyridines with high yields and exceptional diastereo- and enantioselectivities. Key to the success is the introduction of a chiral amine which is incorporated into the pyridine ring by transamination during the transfer hydrogenation process, presumably via forming previously unobtainable chiral tetrahydropyridinium intermediate in situ.
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