Aryne Cycloaddition with Stable Munchnones: Synthesis of 9,10-Dihydro-9,10-epiminoanthracenes and Isoindoles

Arynes react with stable munchnones in a [3+2] cycloaddition/[4+2] cycloreversion sequence under mild conditions. The reaction initially affords isoindoles, but in the presence of excess arynes, these isoindole intermediates readily undergo a further aryne [4+2] cycloaddition to afford 9,10-dihydro-9,10-epiminoanthracenes in good to excellent yields. Controlling the reaction conditions to stop at the isoindole stage was attempted but proved difficult and limited. This chemistry further expands aryne dipolar cycloaddition chemistry with mesoionic substrates.