Triflic Acid Mediated Cyclization of Unsymmetrical N-Phenethyl- and N-(3-Indolylethyl)succinimides: Regio- and Diastereoselective Synthesis of Substituted Pyrroloisoquinolinones and Indolizino­indolones

The regio and diastereoselective synthesis of 1 or 2 alkyl-substituted pyrroloisoquinolinones and indolizinoindolones by triflic acid mediated cyclization via an electrophilic activation of unsymmetrical succinimide carbonyl groups followed by the reduction of fused cyclic N-acyliminium ion is reported. This strategy successfully furnished the pyrroloisoquinolinone and indolizinoindolone derivatives in regioand diastereoselective manner. The steric factor dictates the regioselectivity in N-phenethyl unsymmetrical succinimides and electronic factor seems to dictate the regioselectivity in N-(3-indolylethyl) unsymmetrical succinimides.