Synthesis of Tetracyclic Benzoxazolo-indol-3-ones from Isatogens and Arynes through a [3 + 2]-Cycloaddition and Skeletal Reorganization.

The construction of an unprecedented tetracyclic benzoxazolo-indol-3-one scaffold has been executed through the [3 + 2]-cycloaddition of isatogens with arynes. The initially formed benzisoxazolo-indol-3-one intermediate undergoes a skeletal reorganization through a 1,3-sigmatropic shift/retro-Mannich reaction with the net formation of one C-N and two C-O bonds. The Lewis acid-catalyzed allylation of some of the resulting benzoxazolo-indol-3-ones resulted in oxazepino-indolones with promising photophysical properties.