Eco-friendly synthesis of condensed nitrogen heterocycles A brief experience from our group

In order to develop eco-friendly syntheses of condensed nitrogen heterocycles, solvent-free syntheses on solid acidic catalysts and aqueous reactions using a phase transfer catalyst (PTC) were successfully carried out. The catalysts used were (i) TLC-grade silica gel G (SiO2), (ii) SiO2 doped with 10 mol% phosphoric acid (H3PO4-SiO2), (iii) Montmorillonite K10 clay (K10), (iv) acid-washed K10 clay (acid-clay), (v) K10 doped with one equivalent (with respect to substrate) of tosic acid (TsOH-K10) and (vi) cetylpyridinium bromide (CPB) (5 mol%) as the PTC. The reactions were carried out at room temperature (rt), at 60-70 degrees C (oven) or under microwave irradiation (MWI).