Synthesis of 5H‐imidazo[5,1‐a]isoindole: Photocyclization of N,N′ ‐bis(o‐chlorobenzyl)imidazolium chloride and N‐(o‐chlorobenzyl)imidazole

Abstract

AbstractA N‐heterocyclic compound containing two hetero atoms, imidazo[5,1‐a]isoindole, was synthesized in 40% yield by the intramolecular photocyclization of N,N'‐bis(o‐chlorobenzyl)imidazolium salts 1 in water (neutral or pH ∼4) or of N‐(o‐chlorobenzyl)imidazole 2, in aqueous acid (pH −4). However, the photocyclized compound 3 was not formed effectively in basic aqueous solution (3 equivalents of sodium hydroxide or pyridine) or in acetonitrile by the photochemical reaction of N,N'‐bis(o‐chlorobenzyl)imidazolium salts 1 or N‐(o‐chlorobenzyl)imidazole (2).