Synthesis of Cyclic Conjugated Polyolefins

Abstract

Considerable interest is attached to the properties of cyclic conjugated polyolefins¹, and in a number of studies we have been exploring possible routes to analogues and derivatives of such mono- and bi-cyclic structures as those of cyclo-octatetraene and azulene. In attempts to prepare the azulene analogue (I), for which the name ‘heptalene’ is suggested, the ethyl (0: 5: 5)-bicyclo-duodecatriene carboxylate (II) was submitted to vapour-phase dehydrogenation by the method of Linstead, Millidge, Thomas and Walpole². The main product of this reaction, however, was a mixture of dimethyl-naphthalenes, formed through rearrangement of the carbon skeleton. In an attempt to prevent such rearrangement, a higher speed vapour-phase dehydrogenation technique was evolved, which allowed very brief contact with the catalyst and rapid removal of the products from the zone of the reaction. Under these conditions the product of reaction was a deep blue oil from which azulene-like material was extracted in small yield with 85 per cent phosphoric acid, and regenerated from solution by addition of water.