Lawesson’s Reagent and Microwaves: A New Efficient Access to Benzoxazoles and Benzothiazoles from Carboxylic Acids under Solvent-Free Conditions - Seijas, Julio A; Vázquez-Tato, M Pilar; Carballido-Reboredo, M Raquel; Crecente-Campo, José; Romar-López, Lucía (Synlett, 2007)