Iron(III) Salt-Catalyzed Nazarov Cyclization/Michael Addition of Pyrrole Derivatives

The Nazarov cyclization of two types of pyrrole derivatives was effectively catalyzed by 5 mol% alumina-supported iron(111) perchlorate [Fe(ClO4)(3)center dot Al2O3] which provided the desired cyclization with high trans selectivity in good to excellent yield. The cyclized product was next reacted with a vinyl ketone in the presence of the same iron salt to afford the corresponding Michael product. A sequential type Nazarov/Michael reaction of pyrrole derivatives has also been accomplished; the synthetic route to 4,5-dihydrocyclopenta[b]pyrrol-6(1H)-one derivative 5 or 5,6-dihydrocyclopenta[b]pyrrol-4(1H)-one derivative 6 has thus been established using a very economical iron catalyst.