Selectivity\nin the Formal [2 + 2 + 2] Cycloaromatization\nof Enyne–Allenes Generated by the Alder-ene Reaction from Triynes

1,3-Diynyl propiolates undergo the Alder-ene reaction\nto generate\nenyne–allenes, which participate in the Diels–Alder\nreaction to provide products of a formal [2 + 2 + 2] cycloaromatization\nof three alkynes. Without an external alkyne, enyne–allene\nreacts with one of the alkyne moieties of 1,3-diynyl propiolate,\nwhereas external alkynes can be used to trap enyne–allene to\nprovide various arene products. The substituents on the dienophilic\nalkynes have a profound impact on their reactivity. In this Diels–Alder\nreaction, 1,3-diynes display higher reactivity than monoynes; thus,\nan excess amount (4–5 equiv) of external monoynes needs to\nbe employed to get good product selectivity.