Room-temperature synthesis of m-benzyne

For over a century, scientists have been fascinated by the unique electronic, structural and bonding properties of the three isomers of benzyne, a highly reactive organic intermediate derived from benzene by removing two hydrogen atoms. Although o- and p-benzynes have been extensively studied following the establishment of reliable synthetic methods to prepare them, m-benzyne in the ground state has remained experimentally inaccessible. We report herein the room-temperature and atmospheric-pressure synthesis of m-benzyne in solution. Experimental and theoretical investigations revealed that owing to the inner bond inside the benzene ring between C1 and C3 atoms, m-benzyne behaves as a potent electrophile with a Mayr’s electrophilicity parameter E of around −2 but shows weak free-radical character. The bonding appears similar to the inverted σ-bond, the so-called charge-shift bond, in [1.1.1]propellane. By utilizing the unique bonding character of m-benzyne, we established halogenations and C–N and C–C coupling reactions, as well as a successive m-benzyne generation and trapping sequence that provides access to 1,3,5-trisubstituted benzenes. While facile methods to prepare o- and p-benzynes exist, m-benzyne in the ground state has remained experimentally inaccessible. Now, the room-temperature and atmospheric-pressure synthesis of m-benzyne in solution is reported. Experimental and theoretical investigations reveal that m-benzyne behaves as a potent electrophile but shows weak free-radical character.