Mild and efficient synthesis of benzoxazoles, benzothiazoles, benzimidazoles, and oxazolo[4,5-b]pyridines catalyzed by Bi(III) salts under solvent-free conditions

A series of benzoxazoles, benzothiazoles, benzimidazoles, and oxazolo[4,5-b]pyridines was efficiently synthesized from the reactions of o-aminophenols, o-aminothiophenol, o-phenylenediamines, and 2-amino-3-hydroxypyridine with orthoesters in the presence of catalytic amounts of Bi(III) salts, such as Bi(TFA)(3), Bi(OTf)(3), and BiOClO4 (.) xH(2)O under solvent-free conditions. The remarkable features of this new protocol are high conversion, very short reaction times, cleaner reaction profiles under solvent-free conditions, straightforward procedure, and use of relatively non-toxic catalysts.