PhD Theses.Alkenes are excellent platform chemicals that can undergo various transformations to generate valuable compounds with a range of industrial applications. In recent years, photocatalysis has been increasingly applied in organic synthesis as a unique way of generating radical intermediates that are otherwise not easily accessible. While alkene activation by single electron transfer (SET) oxidation have been studied extensively for photocatalytic hydrofunctionalizations, examples involving SET reduction to the anionic radical species is scarce and the methods are limited by a narrow scope. Unless highly reducing systems were employed, photoreduction of less-activated alkenes bearing one electron-withdrawing group has not been reported to date. Thus, there is a need for new strategies to perform reductive transformations of simple alkenes.
As an alternative to these methods that require either highly oxidizing or reducing conditions, we hypothesized that a different alkene activation strategy could be developed by exploiting hydrogen atom transfer (HAT) chemistry. Our developed photoreduction strategy (Chapter 2) is applicable to over 20 substrates including methyl cinnamate derivatives and other synthetically useful alkenes. Through experimental and computational studies, we have confirmed that the transformation is enabled by an unprecedented hydrogen atom transfer from the oxidized Hantzsch ester to the alkene substrates. The findings from our investigation have driven us to explore other photocatalytic transformations of electron-deficient alkenes. A systematic study was carried out towards developing E to Z isomerization strategies that rely on substrate activation, omitting the need of pre-functionalization (Chapter 3). The last part of this thesis describes our α-selective hydroaminoalkylation protocol for accessing beta-amino acids from a variety of methyl cinnamate and aniline analogues (Chapter 4). This methodology has been successfully applied to styrenes, proving its versatility to generate functionalized amines in a single step
