Change of Connectivity on Catenane Ring:  Ring Expansion by Annulation−Ring Scission Sequence

[reaction: see text]. Ring expansion of a catenane without destruction of the interlocked structure was attained by Diels-Alder reaction followed by ozonolysis. Annulation by Diels-Alder reaction introduced a C4 fragment onto the ring, and the ozonolysis scissored the resulting double bond to expand the catenane ring. The annulation-ring scission sequence provides a general approach for changing the connectivity on a catenane ring without destroying the interlocked structure.