Fluoro‐Ene Reaction Versus [2+2] Cycloaddition in the Thermal C2–C6 Cyclization of Enyne‐Allenes: An Experimental and Theoretical Investigation

Abstract A series of fluoroalkyl‐substituted enyne‐allenes have been synthesized by a new route with the aim of elucidating the possibility of a fluoro‐ene reaction via an intermediate fulvenyl diradical generated in the thermal C 2 –C 6 (Schmittel) cyclization reaction. As a result of the strong C–F bond, fluorine atom transfer was not observed. Instead, 1 H ‐cyclobuta[ a ]indenes were formed in good yields despite the high strain energy. DFT calculations at the B3LYP level of theory indicated that although the fluoro‐ene reaction is the most exothermic reaction available, cyclobutene formation is kinetically favored over the [1,5]‐fluorine shift by 5–15 kcal mol –1 in various model compounds.