Regioselective Synthesis of 3-Carbo-5-phosphonylpyrazoles through a One-Pot Claisen-Schmidt/1,3-Dipolar Cycloaddition/Oxidation Sequence

International audienceA one-pot reaction involving an aldehyde, a methyl ketone, and the Bestmann-Ohira reagent has been developed for the synthesis of variously substituted 3-carbo-5-phosphonylpyrazoles. Our synthetic methodology features a domino Claisen- Schmidt/1,3-dipolar cycloaddition/oxidation sequence,which leads to the target compounds in excellent yields. We further demonstrated that this unprecedented sequence could also be combined with a copper-catalyzed azide- alkyne cycloaddition in a one-pot, four-step cascade process generating five new bonds and two heterocyclic rings