Unexpected Dealkylation During Nucleophilic Substitution: Synthesis of 2- N, N-Dialkylamino Benzoxazoles and Benzothiazoles

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Mild reaction conditions are described for the preparation of a number of 2-alkyl- and 2-arylaminobenzoxazoles and benzothiazoles from 2-chlorobenzoxazole and 2-chlorobenzothiazole and N-methyl or other simple N-alkyl tertiary amines. The reaction proceeds neat or in THF solution and involves dealkylation of the amine reactant by nucleophilic substitution by chloride. In the case of N-methylpyrrolidine and N-methylpiperidine demethylation was not observed and the major product was formed by ring opening to give chlorobutyl- and chloropentyl-methylamino substituted benzoxazoles and benzothiazoles. Treatment of the chlorobutyl derivative with iodide in acetone afforded the new 1 H,2 H,3 H,4 H,5 H-[1,3]diazepino[2,1- b][1,3]benzoxazol-6-ium ring system.