Photocatalytic Transition‐Metal‐Free Direct 3‐Acetalation of Quinoxaline‐2( 1 H )‐ones

Comprehensive Summary A general transition‐metal‐free visible‐light‐promoted 3‐acetalation reaction of quinoxaline‐2(1 H )‐ones was developed under mild conditions. By employing 1,2,3,5‐tetrakis(carbazol‐9‐yl)‐4,6‐dicyanobenzene (4CzIPN) as an inexpensive photocatalyst, and glyoxylic acid acetal as a radical source, various acetalated quinoxaline‐2(1 H )‐ones were constructed in moderate to good yields. Moreover, the versatility of this protocol is highlighted by the successful application in the late‐stage modification of drug molecules and the various functionality transformations. The excellent antitumor activity of the acetalated product demonstrated that this streamlined and sustainable approach could have emerged as a powerful strategy for structural modification in medicinal chemistry.