Iodine-Catalyzed Regioselective Synthesis of Multisubstiuted Pyrrole Polyheterocycles Free from Rotamers and Keto–Enol Tautomers

A highly
regioselective iodine-mediated cascade reaction for the
synthesis of multifunctional polyheterocyclic systems is developed
by employing 3-(2-oxo-2-arylethylidene)­oxindoles and 1,4-benzoxazinone
as starting materials. The polyheterocycles are skillfully embraced
with oxindole, pyrrole, and coumarin scaffolds, which are well-known
for their enriched biological activity. The current approach worked
under mild reaction conditions. The reaction afforded a single product,
and no rotameric and keto–enol isomeric products are formed.
The method is environmentally benign and atom-economical, and the
only side product of this reaction is water. This protocol obviates
the purification techniques such as column chromatography for the
isolation of the products. The products were isolated by decantation
of the solvent or by recrystallization. The reaction proceeds through
inter- and intramolecular C–C and C–N bond formation.