Photochemical cyclisation of phthalimide Mannich bases

Abstract

Ultraviolet irradiation of Mannich bases derived from phthalimide, formaldehyde, and a secondary amine leads to cyclised products containing a new imidazolidine ring. The reaction is much less efficient when the secondary amine has an aromatic group adjacent to the nitrogen atom. Exceptionally, the Mannich base derived from 3-pyrroline does not cyclise but undergoes an internal oxidation–reduction reaction to give a substituted pyrrole.