Allylic and Retro‐Allylic Rearrangements upon Bromination of 8,9‐Substituted 4,4,6‐Trimethyl‐4H‐Pyrrolo[3,2,1‐ij]Quinoline‐1,2‐Diones. New Aspects and Synthetic Applications

Abstract

AbstractBromination of 4,4,6‐trimethyl‐4H‐pyrrolo[3,2,1‐ij]quinoline‐1,2‐diones containing an allylic moiety withN‐bromosuccinimide (NBS) in carbon tetrachloride in the presence of benzoyl peroxide (BPO) and in DMF solution were studied. When using an equimolar amount of NBS in the BPO‐CCl4system, the reaction proceeds regioselectively and standardly at the methyl group at position 6 with the formation of 6‐bromomethylene derivatives. In the NBS‐DMF system, monobromination proceeds at position 5 with the migration of a multiple bond by the allylic rearrangement. With a twofold excess of NBS, in both cases a (Z)‐5‐bromo‐6‐bromomethylene derivative is formed. The 5‐monobromine isomers undergo retro‐allylic rearrangement inN‐ andS‐alkylation reactions, resulting exclusively in 6‐N‐alkyl and 6‐S‐alkyl derivatives, respectively. Similar products are formed by the same reactions with the use of 6‐bromomethylene derivatives.