Iodine promoted annulation reaction for selective construction of Spiro[indene-2,1′-pyrido[4,3-b]indole] and Benzo[5,6]pyrrolo[3′,2': 3,4]cyclohepta[1,2-b]indole

Abstract

I2 promoted cycloaddition reaction of 2-hydroxy-2-(indol-3-yl)-indane-1,3-diones with the in situ generated β-enamino esters, which were generated from the reaction of arylamines and dialkyl but-2-ynedioates, showed very interesting molecular diversity. In the presence of 30 % mmol iodine, the reaction in acetonitrile at 80 °C resulted in the novel spiro [indene-2,1′-pyrido [4,3-b]indole] derivatives in good yields. On the other hand, in the presence of 80 % mmol iodine, the reaction in acetonitrile at 60 °C gave the ring-expanded benzo [5,6]pyrrolo [3′,2':3,4]cyclohepta [1,2-b]indole derivatives in moderate to good yields. Additionally, the similar iodine-promoted reaction of 2-(indol-2-yl)diarylmethanols and β-enamino esters gave the unique 1,1,2-triphenyl-2,9-dihydropyrido [3,4-b]indoles in satisfactory yields. A plausible domino annulation mechanism was rationally proposed for the formation of various polycyclic compounds.