Controlled Formation and Unusual Reactivity of Cyanohexatriyne (HC7N), a Synthetically Challenging Interstellar Cyanopolyyne.

Abstract

Cyanohexatriyne (HC₇N), a highly unstable member of the interstellar cyanopolyyne family, has long resisted synthetic access. We report the first reproducible formation of HC₇N 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 HC₇N was characterized in solution and shown to undergo a rapid and stereoselective conjugate addition with diethylamine to the terminal C≡C triple bond.