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

摘要

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, 1H-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 kcalmol~(-1) in various model compounds.