Synthesis of Indolinones from Arynes and Amino Acid Esters

Significance

Reported is the synthesis of 2-phenylindolin-3-ones 3 via the cycloaddition of arynes 4 (generated in situ from 1) with amino esters 2. The initially expected product 5 could not be isolated since rapid tautomerization to 6 and ene ­reaction with a second equivalent of aryne follows to give 3. Interestingly, when aspartic acid methyl ester was used as a substrate, indolinone aryl­idene 7 was isolated in 51% yield, presumably by hydrogen transfer from 6 to benzyne, giving 7 and benzene.