The regioselective cyclopolymerization of two structurally different 1,7-octadiynes, i.e. of 1,4-dihexyloxy-2,3-dipropargylbenzene (M1) and (R,R)/(S,S)-4,5-bis(trimethylsilyloxy)-1,7-octadiyne (M2) has been achieved with the modified Grubbs-Hoveyda-type metathesis initiator Ru(NCO)(2) (IMesH(2))(=CH-(2-(2-PrO)C(6)H(4))) (I1, IMesH(2) = 1,3-dimesitylimidazolidin-2-ylidene) and with a series of Schrock initiators in the presence of quinuclidine, yielding conjugated polymers consisting virtually exclusively of 1,2-cyclohex-1-enylenvinylene units. In contrast to I1, Mo(N-2,6-(2-Pr)(2)C(6)H(3)) (CHCMe(2)Ph)(OCHMe(2))(2) (I3) allows for establishing a living polymerization with M2 in the presence of quinuclidine. The structure of the polymers, which represent highly soluble and stable poly(acetylene) analogues, Was confirmed by comparing the (13)C NMR shifts of model compounds with those of the corresponding polymer. Poly(ene)s that are virtually solely based on six-membered repeat units show a bathochromic shift in UV-absorption compared to poly(ene)s based on six- and seven-membered rings.