Complexity from simplicity: intramolecular meta-thermocycloadditions of benzene rings via Wheland intermediates

Dearomative cycloadditions are powerful synthetic transformations utilizing aromatic compounds for cycloaddition reactions1-4. Diverse complex three-dimensional architectures could be built upon the flat land of aromatic compounds. In addition, such transformations are atom- and step-economical and, thus, have been widely applied to the preparations of complex biologically relevant compounds5-7. For the ubiquitous and most studied yet challenging benzene ring systems8, ortho- and para-cycloadditions are feasible both photochemically and thermally, while the meta-cycloadditions are still limited to the photochemical processes from the 1960s9,10. Herein, we have realized the meta-thermocycloadditions of benzene rings in an intramolecular fashion. The reaction was proposed to proceed via [4π+2π] cycloadditions of Wheland intermediates from the electrophilic dearomatization of benzene rings. A broad spectrum of readily available C(sp2)-rich aniline-tethered enynes were transformed into C(sp3)-rich 3D complex polycyclic architectures simply by stirring in TFA. Moreover, the reaction could be performed in gram-scales and the products could be diversely elaborated.