A novel rearrangement forming 4,5,6,11-tetra-hydrobenzo[6,7]cycloocta[1,2-b]thiophen-6,11-imines

Exposure of the spirocyclic isoindolines 9 and 16 and the spirocyclic ether 23 to HBr gas in methylene chloride at 0°C leads to the formation of the bridged heterocycles 10, 17, and 24 respectively. These novel rearrangements probably occur via retro-Mannich fragmentation and subsequent intramolecular Mannich reaction on the thiophene ring.