One-Pot, Three-Component Approach to the Synthesis of 3,4,5-Trisubstituted Pyrazoles

An operationally simple and high
yielding protocol for the synthesis
of polyfunctional pyrazoles has been developed through one-pot, three-component
coupling of aldehydes, 1,3-dicarbonyls, and diazo compounds as well
as tosyl hydrazones. The reaction proceeds through a tandem Knoevenagel
condensation, 1,3-dipolar cycloaddition, and transition metal-free
oxidative aromatization reaction sequence utilizing molecular oxygen
as a green oxidant. The scope of the reaction was studied by varying
the aldehyde, 1,3-dicarbonyl, and diazo component individually.