Catalytic reactions of pyridinium and iminium ions
Date
2020
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Publisher
University of Delaware
Abstract
The dissertation focuses on transition metal catalysis of cationic species to make C-C bonds. ☐ Chapter 1 describes a nickel-catalyzed Suzuki-Miyaura cross-coupling of benzylic pyridinium salts. The pyridinium salts act as electrophiles in the cross-coupling reaction. By utilizing a single-component catalyst, the pyridiniums cross-couple effectively with aryl boronic acids to deliver diarylmethanes. Heteroaryls on both cross-coupling partners can be well tolerated. Notably, many pharmaceutically relevant diarylmethanes have high heteroatom contents. However, these heteroaryl substituted molecules have been largely neglected in the traditional cross-couplings. Moreover, a broad scope of functional groups can be incorporated as well. ☐ Chapter 2 describes a nickel-catalyzed cross-coupling of benzylic pyridinium salts with vinyl boronic acids or esters. This method enables access to a variety of 1,3-disubstituted allylic molecules. Heteroaryl substitution can be well tolerated. Both aromatic and aliphatic alkenes can be formed with good regioselectivity. A metal-free variant has also been observed, affording the desired products albeit in lower yields than the nickel-catalyzed conditions. ☐ Chapter 3 describes an enantioselective copper catalyzed alkynylation reaction of cyclic iminium ions to deliver cyclic amines bearing ⍺-stereocenter. Notably, this is a first example of an unstabilized cyclic iminium ion used in enantioselective alkynylation. Previous methods have been focused on cyclic iminium ions stabilized by resonance. By using CuI and a PhPybox ligand, good yield and selectivity were observed. Under the mild reaction, a wide range of functional groups can be incorporated.
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Keywords
Catalytic reactions, Pyridinium, Iminium ions