Fragmentation – Ring expansion

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.

M. A. Drahl, M. Manpadi and L. J. Williams, Angew. Chemie – Int. Ed., 2013, 52, 11222–11251.