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

Abstract Bromination of 4,4,6‐trimethyl‐4 H ‐pyrrolo[3,2,1‐ ij ]quinoline‐1,2‐diones containing an allylic moiety with N ‐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‐CCl 4 system, 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 in N ‐ and S ‐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.