Efficient Parallel Synthesis of Privileged Benzopyranylpyrazoles via Regioselective Condensation of β-Keto Aldehydes with Hydrazines

Abstract

In this study, the practical construction of a pilot library with benzopyranylpyrazole, a novel core skeleton synthesized through the recombination of privileged structures, benzopyran and pyrazole, was successfully conducted through the efficient utilization of solution-phase parallel synthesis using solid-phase reagents and solid-phase parallel synthesis. We have also developed a novel procedure for the synthesis of benzopyranylpyrazoles via regioselective condensation of substituted hydrazines with beta-keto aldehydes. The diversity of this core skeleton was expanded by the regioselective introduction of alkyl- and aryl-substituents at the R(1) diversity point on the pyrazole moiety and by the introduction of piperazine on the benzopyran substructure, which provide the R(2) diversity point. Lastly, the introduction of a nitro group on the benzopyran moiety was found to accelerate the nucleophilic aromatic substitution of piperazine and provide the R(3) diversity point at the aniline moiety through the reduction of the nitro group. In this pilot library, we only focused on the diversification at the R(1) position with either the R(2) or R(3) position, and thus maximized the diversity through the rational selection of building blocks using chemoinformatics. Overall, a 192-member benzopyranylpyrazole pilot library was constructed with an appending potential for further diversification. The average purity of the library is 87%.