The effect of pressure on the trimerization and Diels‐Alder reaction of cyanoacetylene. Synthesis and reactivity of 2,3,5‐tricyanobicyclo[2.2.0]hexa‐2,5‐diene („tricyano Dewar benzene”)

The trimerization of cyanoacetylene (1a) and the Diels‐Alder reaction of 1a with 1,3‐cyclohexadiene (2) show a powerful pressure‐induced acceleration which allows the reaction temperature to be reduced from 160°C at 1 bar to 40°C at 12 kbar or from 100deg;C at 1 bar to room temperature at 7 kbar. At high pressure thermally unstable intermediates like the tricyano Dewar benzene 12 generated in the trimerization of 1a or the primary adduct 3a formed in the Diels‐Alder reaction of 1a with 2 were isolated.