Solvent free and Montmorillonite K10 catalysed domino reactions for the synthesis of pyrazoles with alkynylester as a dual synthon
A highly regioselective, solvent free and montmorillonite K10 clay catalysed domino process with an unprecedented ring closing C-C bond formation reaction is described for the synthesis of new class of 1,3,4-trisubstituted and 1,4-disubstituted pyrazole derivatives. The reaction proceeds via a nucleophilic attack of enamine from an intermediate on the β carbon of an amino acrylate. Experimental outcome has clearly revealed that the organic solvents produce adverse effect for the pyrazole formation and oxidative condition in the presence of the reusable clay favours the 1,3,4-trisubstituted pyrazole formation. The clay in the presence of N-bromosuccinamide (NBS) catalyst gives the 1,4-disubstituted pyrazole after a pyrolytic cleavage at elevated temperature.