structural studies of cyclocarbons have been limited to cryogenic temperatures . Carbyne is predicted to be a 1D semiconductor with outstanding tensile strength and thermal conductivity , and its properties have been deduced by extrapolation from experimental studies of monodisperse polyynes, which consist of chains of sp 1 -carbon atoms with bulky groups at both ends . The longest previously reported polyynes of this type have chains of 48 sp 1 -carbon atoms . These polyynes were synthesized using a strategy in which the final step is the oxidative Glaser of a fragile hydrogen-terminated polyyne intermediate, R-(CºC)n-H, with half the length of the final product, R-(CºC)2n-R (Fig. ). There are four major drawbacks to this conventional strategy for polyyne synthesis: 1) The instability of the terminal polyyne intermediate limits the efficiency of the final Glaser reactions; 2) The stepwise synthesis of this terminal polyyne intermediate can be laborious; 3) The final Glaser coupling step can be accompanied by loss of acetylenic units, resulting in shorter polyyne by-products that are difficult to separate from the desired product ; 4) The stabilizing effect of the endgroups diminishes dramatically with increasing chain length. Supramolecular encapsulation has previously been demonstrated to enhance the stability of polyyne dumbbells, by threading them through macrocycles to form rotaxanes . Polyyne [2]rotaxanes can be synthesized using active metal templates , but there has been no method available for threading more than two macrocycles onto a polyyne chain. Here we show that, masked alkyne equivalents (MAEs) provided an efficient 'precursor route' to polyynes (Fig. ). Two types of masked building blocks are required to construct long polyyne polyrotaxanes: one with two reactive termini and one with a stopper at the end. We chose dicobalt tetracarbonyldiphenylphosphinomethane, Co2(CO)4dppm, as the masking group 33 , because it is bulky enough to act as a temporary stopper, to prevent unthreading of the macrocycles, and because it is unaffected by the reaction conditions of Glaser coupling. Here we show that these masked polyynes can be unmasked efficiently under mild conditions. This precursor route circumvents all four of the drawbacks to the conventional route listed above, and it provides access to much longer polyynes than synthesized previously.