AbstractAn improved synthesis of CTMC is described. This cyclobutene is thermally stable towards electrocyclic ring opening. Its reactivity is explored and a number of radical adducts are described. A more complicated picture is observed with various nucleophiles. The strong dienophilic character of CTMC is illustrated by numerous examples. CTMC reacts well as a dipolarophile with diphenylnitrone, diphenylnitrilimine and diazoalkanes. The high reactivity of this cyclobutene is due to its inherent polarity and strain.