An Improved Large-Scale Synthesis of Benz[cd]indol-2(1H)-one and 5-Methylbenz[cd]indol-2(1H)-one

An improved synthesis of benz[cd]indol-2(1H)-one (3) and a novel synthesis of 5-methylbenz[cd]indol-2(1H)-one (4) utilizing analogous methodology is reported. Starting from 1,8-naphthoic anhydride and 4-nitro-1,8-naphthoic anhydride, an appropriately substituted N-(2,4-dinitrophenoxy)naphthalimide is prepared. Subjecting these intermediates to improved Lossen rearrangement conditions yields 3 and 5-nitrobenz[cd]indol-2(1H)-one (11). 11 is converted to 5-iodobenz[cd]indol-2(1H)-one (13) by standard reduction and diazonium chemistry. 13 is converted to 4 by palladium(II)-catalyzed coupling of the aryl iodide with methyl-Grignard.