Unexpected regiochemistry in [3+2] cycloaddition reaction of azomethine ylides of indenoquinoxalinone series to arylidene malononitriles
1,3-Dipolar cycloaddition of azomethine ylides generated in situ from proline and indenoquinoxalinones occurred at the double bond of arylidene malononitriles upon heating in isopropanol, leading to the respective spirocyclic adducts with cis orientation of the aryl substituent and the quinoxaline moiety. The regioselectivity of this process depended on the electron donor-acceptor properties of substituents in the aromatic ring of the dipolarophile molecule. Analogous reaction involving azomethine ylide derived from sarcosine produced adducts with a trans relationship of the most sterically demanding substituents.