Construction of All-Carbon Quaternary Stereocenters via Sequential Photoactivation/Isothiourea Catalysis.

Highly enantioselective [4 + 2] cyclizations of azadienes with in situ generated ketenes were developed through sequential visible-light photoactivation/isothiourea catalysis, which offers a novel approach for the creation of all-carbon quaternary stereocenters through disubstituted C1-ammonium enolates. The visible-light-induced sustained release of reactive ketene species through Wolff rearrangement of α-diazoketones is crucial for achieving high levels of chemical efficiency and stereoinduction.