Development and Mechanistic Understanding of Photochemical Reactions

The doctoral thesis of Ana Bahamonde describes the development and mechanistic understanding of photochemical organocatalytic reactions. Initially, she focused on designing new chemical transformations that relied on the formation of electron-donor acceptor (EDA) complexes. Specifically,  an enamine-mediated enantioselective photochemical α-alkylation of ketones with electron-poor alkyl bromides was the developed. Subsequently, this EDA complex-mediated strategy was expanded to the photochemical alkylation of indoles with electron-poor alkyl bromides.

The second part of her PhD work was characterized by a progressive transition from reaction development towards a mechanistically-oriented approach. In particular, she focused on detailed mechanistic studies of some photochemical enantioselective transformations previously developed in the Melchiorre group. They studied the mechanism of the enamine-mediated photochemical α-alkylation of aldehydes. Quantum yield measurements revealed that a radical chain mechanism was operative. Moreover, kinetic studies established the trapping of the carbon-centered radical by the enamine, to form the carbon-carbon bond, as the turnover-limiting step. Additionally, the turnover-limiting step of the iminium ion-mediated radical conjugate addition to β,β-disubstituted cyclic enones which had been previously developed by the group was uncovered.