Synthesis and electrochemical properties of 4-phenyl-1-buten-3-yne-1,1,2-tricarbonitriles and tricyanoacrylates

The reaction of phenylacetylenes 4a–h with copper(I) acetate (5) and TCNE (tetracyanoethylene) in THF/acetonitrile gave 4‐phenyl‐1‐buten‐3‐yne‐1,1,2‐tricarbonitriles 6a–h. 4i did not react to give 6i. The phenylacetylenes 4b–i were prepared by a two‐step synthesis starting from the corresponding phenyl halides 1b–i. The tricyanoacrylates 8 were synthesized from the corresponding cyanoacetates 7, TCNE and catalytic amounts of pyridine in THF. – Cyclovoltammetric investigations showed that the butenynes 6 and the tricyanoacrylates 8 are strong electron acceptors which can be easily reduced. The radical anions 6˙− are unstable in aceto‐nitrile and react irreversibly with 6 to give oligomeric anions 6 n˙−. Only 4‐(2,4,6‐trimethoxyphenyl)‐1‐buten‐3‐yne‐1,1,2‐tricarbonitrile (6h) is reduced to a radical anion 6h˙− which associates with 6h in a reversible follow‐up process to form a dimeric anion 6h 2˙−. By contrast, the tricyanoacrylates 8 can be reversibly reduced to their respective radical anions and dianions.