Distortion-controlled 1,2-dicarbene reactivity of 3-triflyloxybenzynes: a theoretical approach

Abstract

A high reactivity of 3-triflyloxybenzynes in the macrocyclization reaction with tetrahydrofuran (THF) was recently reported by Cheng et al. and it was analyzed by our group using DFT calculations. We found that the transformation proceeds through an overlooked pathway arising from 1,2-dicarbene reactivity and via the intermediacy of a de-aromatized cyclic allene and not the ortho-triflyloxy aryl anion suggested by Cheng et al. The 1,2-dicarbene reactivity of the arynes was proved using natural bond orbital, electron localization function, and frontier orbital analysis. The stability of various 1,2-dicarbene-type benzynes was determined by two key factors, first, the spatial extent of the donating orbital on the C2 atom which is dependent on the π-donation ability of the substituents, and second, the electron occupancy of the orbital which is in turn dependent on the σ-donation ability of the substituents. The reactivity of various 3-triflyloxybenzynes were found to be dependent on the distortion magnitude required to reach the transition state.