An interesting substituent effect on the acid‐catalyzed skeletal rearrangement of seco‐homocubanes

The acid catalyzed rearrangement of 1-bromotetracyclo[4.3.0.02.503.8]nonan-4-one 1b has been studied. With aqueous HBr, the exclusive formation of 2,7-dibromotricyclo[4.2.1.03.7]-nonan-4-one 4b was observed. This structure was established by X-ray analysis. The divergency in behaviour of seco-homocubane 1b and its 9-ethylene acetal derivative 1a towards acidic reagents reveals a directing effect of the 9-ethylene acetal function on the skeletal rearrangement.