CsF-mediated reaction of diazo compounds with 3-nitroindoles: access to cyano- and phosphonylpyrazolo[4,3-b]indoles

Abstract

A CsF-promoted synthesis of cyanopyrazolo[4,3-b]indoles via a [3+2] cycloaddition reaction of diazoacetonitrile with N-substituted 3-nitroindoles and subsequent elimination of the nitro group has been devised. This protocol delivers diverse cyano-containing pyrazole-fused indoles in good to excellent yields under mild conditions. Besides diazoacetonitrile, the Seyferth–Gilbert reagent (SGR) readily participated in this reaction to provide facile access to phosphonylated pyrazolo[4,3-b]indoles.