Radical Cascade Reaction of Heterocyclic Ketene Aminals with Thiocyanates Promoted by Visible Light: Synthesis of Functionalized Fused 2-Iminothiazolines

Herein, a visible-light-promoted radical cascade cyclization of heterocyclic ketene aminals (HKAs) and thiocyanates was developed to access functionalized fused 2-iminothiazolines. This novel cascade reaction can be realized under only visible-light irradiation without the help of external photocatalysts, oxidants, and additives. These multicomponent cascade reactions demonstrate excellent selectivity for the <i>Z</i>-isomers and ensure the formation of the products only in their isomeric form. Preliminary mechanism investigations demonstrated that HKAs and thiocyanates can form electron donor-acceptor complexes for harvesting the energy of visible light to activate substrates and generate reactive radicals. This protocol can be used for synthesizing various natural-like products such as fused 2-iminothiazolines. This approach demonstrates multiple advantages such as commercially available substrates, convenient operation, environmentally friendly, mild conditions, and an efficient multicomponent reaction (2A + B).