Metal-Free Synthesis of 2-N,N-Dialkylaminobenzoxazoles Using Tertiary Amines as the Nitrogen Source

The unprecedented reaction of tertiary amines with 2(3H)-benzoxazolones has been investigated. In the presence of the Ph3P-I-2 reagent system, the reaction of both acyclic and cyclic aliphatic tertiary amines led to the formation of 2-N,N-dialkylaminobenzoxazoles with the selective cleavage of an alkyl group. Especially, N-(2-iodoethyl)piperazinyl derivatives were rapidly produced in good yields when using DABCO as the nitrogen source. Only in the cases when the nucleophilicity of the substrates exceeds that of the amine, competitive self -condensation of benzoxazolones then proceeds preferentially. P-31{H-1}-NMR study suggested the involvement of an aryloxyphosphonium intermediate and/or possibly 2-iodobenzoxazole which activates the C-2 position of benzoxazolones toward nucleophilic aromatic substitution.