Synthesis and Thermal Rearrangement of 4‐Heterohepta‐1,2,5,6‐tetraenes

4‐Heterohepta‐1,6‐diynes can be rearranged by base catalysis under carefully controlled conditions to the corresponding 4‐heterohepta‐1,2,5,6‐tetraenes. Thermal rearrangment of these tetraenes gives the corresponding dimers by a process in which the rate‐determining step is first order. The rate constants for these reactions have been determined and the relative rates accounted for in terms of an aromatic contribution afforded to the presumed diradical intermediates. In the two cases investigated it was found that when the thermolyses were conducted in the presence of 3 O 2 then cyclic peroxides were formed.