NOTE: Important charges and non-bonding electrons are shown throughout the animation except during the transition phase
Click the structures and reaction arrows in sequence to view the 3D models and animations respectively
Ring sizes greater than 8 are hard to make. Yet 5- and 6-membered rings are easy to make. Once you realise that a fused pair of 6-membered rings is really a 10-membered ring with a bond across the middle, the potential for making medium rings by fragmentation becomes apparent.
All you need to do is make the bond to be broken the 2-3 bond in a 1, 2, 3, 4 electron source-sink rearrangement and the 10-membered ring should appear out of the wreckage of the fragmentation. Above is an example of a decalin that fragments to a 10-membered ring.