Studies on Heterocyclic Compounds. XXXIV. Synthesis of 2-Substituted Aminobenzoxazoles with Nickel Peroxide

Oxidation of N-methyl (or phenyl)-N'-(4-methylpyrid-2-yl) thiourea (Ia, b) with nickel peroxide (Ni-PO) under reflux in benzene or acetonitrile afforded the corresponding ureas (IIa, b). N-(2-Hydroxy-5-methylphenyl)-N'-methylthiourea (IVa) was synthesized by the reaction of 2-amino-4-methylphenol (III) and methyl isothiocyanate in benzene under reflux. However, the reaction of III and phenyl isothiocyanate in benzene under reflux did not afford the thiourea (IVb) but IVb was obtained in ethanol at room temperature. Ni-PO oxidation of thioureas (IVa-f) in acetonitrile at room temperature afforded 2-substituted aminobenzoxazoles (VIIa-f) in good yields. The reaction mechanisms of Ni-PO and thioureas (Ia, b and IVa-f) are discussed.