1,4‐Didehydrobutadiene: The Intermediate in a New Class of Thermally Induced Intramolecular Alkyne Couplings

Nonconjugated diynes can also form diradicals by cyclization. Thermolysis of 1 (R = iPr) initially yields 1,4-didehydrobutadiene 2, which reacts with a hydrogen donor R'H (e.g. solvent) to give the trapping products 3 and 4. The reactivity of 1 is explained by the electronic activation of the alkyne units by the N atoms, a sufficiently small separation of the C atoms to be linked, and a gain in energy upon formation of the σ and π bonds.