Incorporação fotocatalítica de CO2 em moléculas orgânicas

Abstract

Photocatalytic incorporation of CO2 into organic molecules. The fixation of carbon dioxide (CO2) into organic molecules represents a powerful approach to valorize this abundant, renewable, and non-toxic C1 carbon source, while simultaneously enabling access to highly functionalized compounds of synthetic and industrial relevance. In recent years, visible-light photocatalysis has emerged as a sustainable tool to achieve CO2 fixation under mild conditions, thereby expanding the chemical space accessible from simple building blocks. A particularly versatile approach relies on the Reductive Radical–Polar Crossover (RRPCO) mechanism, in which a radical intermediate generated under photocatalytic conditions is converted into a nucleophilic species during the photocatalyst turnover step, which can be intercepted by electrophiles such as CO2. This mechanistic pathway enables the selective formation of C–C bonds with high functional-group tolerance in a single operational step. This work describes three distinct strategies based on the RRPCO mechanism for the incorporation of CO2 into organic molecules, providing access to carboxylic acid derivatives. Chapter I: Visible-Light-Induced multicomponent difunctionalization of styrenes using CO2 and radical precursors. This chapter covers two complementary methodologies for the simultaneous installation of two distinct functionalities on styrene derivatives. In the first approach, sodium sulfinates and CO2 are used as coupling partners to access β-sulfonylated carboxylic acids in good yields and with broad functional group tolerance. Catalyst choice proved crucial: Ru(bpy)3 was optimal for electron-poor styrenes, whereas 4CzIPN performed better with less electron-deficient substrates. Exploiting the sulfone group as a leaving group, a one-pot carboxy-sulfonylation-elimination sequence enabled the α-carboxylation of styrenes to yield α-aryl-acrylates. The second approach is a redox-neutral β-amidation–α-carboxylation protocol using styrenes, CO2, and 1,4-carbamoyl-dihydropyridines under photocatalysis with 4CzIPN. This mild, operationally simple method tolerates diverse functional groups, allows late-stage functionalization of complex molecules, and incorporates both sterically hindered and amino acid–derived carbamoyl radicals, granting access to succinamic acids. Chapter II: Synthesis of α-amino acids by ConPET-mediated CO2 fixation into amides. This strategy enables the selective functionalization of α-C(sp3)–H bonds adjacent to the nitrogen atom in amides through the synergistic combination of Hydrogen Atom Transfer (HAT), consecutive Photoinduced Electron Transfer (ConPET), and RRPCO. CO2 and deuterium were incorporated at the α-position to the amide nitrogen, affording α-amino acids and α-deuterated amides in moderate to high yields. Mechanistic studies revealed that both 3DPAFIPN and its in situ photodegradation products generate highly reactive α-amino carbânions under exceptionally mild conditions, providing insights for future catalyst design and expanding photocatalyst activation concepts. Isotope labeling: In addition, the three developed protocols proved to be versatile tools for the synthesis of isotopically labeled products by enabling the incorporation of 13CO2 into styrenes and amides, resulting in the formation of α-aryl acrylates, succinamic acids, and α-amino acids. These results highlight the potential of RRPCO-based strategies for mechanistic studies as well as for applications in tracer studies, metabolic investigations, and pharmaceutical development.