Cleavage of Unstrained C−C Bonds in Acenes by Boron and Light: Transformation of Naphthalene into Benzoborepin

Naphthalene and acenaphthene with peri 2‐py and BMes₂ (py=pyridyl, Mes=mesityl) substituents have been found to undergo facile phototransformation, cleavage of a C−C bond of naphthalene, and formation of 2‐py‐bound benzoborepins as the major products. Mechanistic pathways of this photoreaction have been established by examination of both excited and ground states by using CASSCF and CASPT2 methods in DFT and time‐dependent DFT calculations. The mesityl to py‐naphthyl charge‐transfer transition and the mesityl migration from the boron atom to the naphthyl moiety drive this unprecedented C−C bond cleavage and boron‐insertion reaction.