Synergistic Visible Light Nanophotocatalysis and Asymmetric Organocatalysis for the Stereoselective α-alkylation of Aldehydes

Carbon dots (CDs) are privileged carbon-based nanomaterials which they have been extensively studied in recent years in catalysis. In fact, their peculiar photoluminescence features have found applications in nanophotocatalysis as well as bioimaging and sensing. Nevertheless, their application as nanophotoredox catalysts in stereoselective transformations is still unexplored. Herein, this study reports the combination of carbon dots as nanophotocatalysts and asymmetric organocatalysis for the stereoselective α-functionalization of aldehydes. Employing various bromo-derivatives as alkylating agents, it achieves the corresponding enantioenriched α-alkylated derivatives with excellent yields (up to 94%) and enantioselectivities (up to 98:2 e.r.). With a series of control experiments, cyclic voltammetry and fluorescence quenching studies, it is possible to postulate a synergistic dual catalytic cycle that involves a photo-oxidative quenching of the excited stated of CDs paired with an enamine activation promoted by the MacMillan organocatalyst followed by radical alkylation. This study successfully demonstrates that carbon dots can efficiently replace metal-based photocatalysts, promoting photoredox catalytic stereoselective transformations even at low concentrations (down to 0.1 mg mL‾¹), paving the way to more sustainable and possibly recyclable catalytic systems.