Controlled Formation and Unusual Reactivity of Cyanohexatriyne (HC ₇ N), a Synthetically Challenging Interstellar Cyanopolyyne

Cyanohexatriyne (HC 7 N), a highly unstable member of the interstellar cyanopolyyne family, has long resisted synthetic access. We report the first reproducible formation of HC 7 N at the milligram scale, enabled by a cobalt–alkyne masking strategy that circumvents the intrinsic instability of extended sp‐carbon chains bearing a terminal nitrile. This approach overcomes the limitations of classical C sp –C sp coupling methods and provides enough material for chemical investigation. The formed HC 7 N was characterized in solution and shown to undergo a rapid and stereoselective conjugate addition with diethylamine to the terminal C≡C triple bond.