Photocatalytic Four-Component Sulfonylation/ Ipso -Spirocyclization of N -Arylpropiolamides with Thianthrenium Salts, DABSO and H2O: Access to 3-Sulfonyl-Azaspiro[4.5]trienones

A visible-light-induced sodium fluorescein-catalyzed four-component cascade reaction of N-arylpropiolamides, aryl thianthrenium salts, DABSO, and H2O has been developed, providing efficient access to diverse 3-sulfonyl-azaspiro[4.5]trienones in moderate to good yields. The reaction accommodates a broad range of aryl thianthrenium salts and propiolamide substrates, tolerating various functional groups. Mechanistic investigations suggest a radical cascade pathway involving the formation of arylsulfonyl radicals, followed by sulfonylation, ipso-spirocyclization, and H2O trapping. The four-component, one-pot nature of this transformation, combined with its mild conditions and operational simplicity, offers a sustainable and step-economical strategy for constructing pharmaceutically relevant azaspiro scaffolds.