A profound change from the classic mechanism of electrophilic aromatic substitution in the gas phase to a novel mechanism, including the hydride transfer in the presence of Cucurilbit[6] uril (DFT prediction)

The DFT B3LYP/6–311+G* calculations were carried out for the reactions ArH / CBr3+Al2Br7− (ArH = PhH, PhNH2, PhNMe2) (I) and ArH / CBr3+Al2Br7−/СО (II) in a gas phase. The same reactions in the presence of cucurbit[6]uril (CB6), were calculated by the DFT B3LYP/6–31G* basis set. The calculations show that the classical mechanism of electrophilic aromatic substitution (EAS) in the gas phase changes abruptly when the reactions are carried out in CB6. Unlike the classical mechanism involving the attack of electrophile on the arene C atom with the formation of the tetrahedral cationic intermediate followed by proton substitution by electrophile, in CB6, the cation attacks the arene H atom resulting in high barrier H / Br exchange (reaction I) or low-barrier carbonylation reaction (reaction II) as the only channel in each case.