Development of Synthetic Routes for Carbon-Carbon and Carbonheteroatom Bond Formation under Solvent- and Catalystfree Conditions

Abstract

The toxicity and volatile nature of organic solvents that are widely used in huge amounts for chemical transformations have posed a serious threat to the environment. With the growing awareness in industry and academia for the sustainable development, the development of solvent-free reaction has received tremendous attention in recent years under the title “Green Chemistry”. Five different chemical transformations viz., aza-Michael addition of amines to α,β-unsaturated acids, Knoevenagel condensation of salicylaldehydes and oaminobenzaldehydes with malononitrile, cascade Knoevenagel-Michael reaction of 4- hydroxy-1-methylquinolin-2(1H)-one, aldehydes and several active methylene compounds, one-pot, three-component reactions for the synthesis of quinazolines and densely functionalized pyrroles have been studied under solvent- and catalyst-free conditions during the present investigation. All the newly synthesized compounds have been characterized using FTIR, 1H NMR, 13C NMR, mass spectral and elemental analyses. Also, structures of a few target molecules have been confirmed by X-ray crystallographic analysis. From the results, it has been observed that, the organic transformations proceed faster and to a high degree of completion when the reaction occurred via homogeneous melt formation. However, the success of the reaction depends on the reactivity of the starting materials. The greener advantages of solvent- and catalystfree reactions over conventional protocols are: easy reaction of poor soluble reactants, short reaction time, high product yield, avoidance of (i) distillation of solvents for reaction, (ii) hazardous solvents in reaction, (iii) solvent evaporation from the reaction mixture, (iv) tedious synthesis of catalysts, (v) solvent usage for catalyst separation.