RING-CHAIN EQUILIBRIUM BETWEEN AN [18]CYCLACENE DERIVATIVE AND A LADDER OLIGOMER

The synthesis of the AB-type Diels-Alder (DA) monomer 12 is reported w hose self-condensation leads to the formation of the linear ladder oli gomer 17 and its cyclic congener 18. 18 is the largest [n]cyclacene de rivative known (n = 18) and can be obtained by thermal treatment of 17 in yields of up to 45 % utilizing the reversibility of the DA cycliza tion involved. 17 can be considered a ''storage form'' for 18.