The formation of polyynes with an odd number of conjugated triple bonds is synthetically demanding, particularly for complex architectures, since most established methods rely on irreversible C-C bond-forming reactions and operate under kinetic control. To address this problem, we have developed the synthesis of triynes via molybdenum-catalyzed alkyne metathesis of diynes, which allows thermodynamic control through reversible cleavage and formation of carbon-carbon triple bonds. We demonstrate the potential of this method through the synthesis of challenging, more complex products, including triyne precursors to 7cumulenes, a pentayne, a heptayne, and dehydrobenzannulene macrocycles containing triynes. The key to the success of the proposed methodology is achieving a balance between the selectivity and reactivity of the molybdenum catalyst with the diyne precursors.
Escudero et al. (Tue,) studied this question.