Photocatalyzed formal carbooxygenation of terminal alkynes

An efficient visible-light-induced formal carbooxygenation of N-arylsulfonylamido alkynes has been developed. This metal-free transformation allows for the rapid assembly of 4-formyl benzothiazines from readily available substrates through the sequential formation of C–C and CO bonds. 18O isotope tracing revealed that the formyl oxygen is derived from aerial oxygen.