Intramolecular Cyclization of the ortho‐Substituted N‐arylquinone Imines under Basic and Thermal Conditions

The S(O,N)‐benzyl ethers of N‐arylquinone imines undergo cyclization under the action of bases to form products of the benzothiazol, benzoxazole, and benzimidazole series, while under thermal conditions they undergo a non‐catalyzed rearrangement to form spiro‐cyclohexadiene derivatives of benzazines. The benzimidazole, spirobenzothiazine, and spirobenzoxazine structures were supported by the x‐ray diffraction method. The possibility of intramolecular photochemical cyclization was investigated; ortho‐S(O,N)‐benzyl‐substituted N‐arylquinone imines show high photostability under UV irradiation. The features of the cyclization processes of quinone imine derivatives were revealed by DFT calculations using the wB97XD/6‐311++G** method. The dependence of the N‐arylquinone imines benzyl ethers cyclization reaction pathway on the conditions is established. Under basic conditions, cyclization proceeds through the formation of a dihydro azole ring; under thermal conditions, cyclization proceeds through the formation of a spirane azine ring; under photochemical conditions, neither direct cyclization nor reverse reaction occur.