Tandem Aza Michael Addition–Vinylogous Nitroaldol Condensation: Construction of Highly Substituted <i>N</i>-Fused 3-Nitropyrazolopyridines

Abstract

A base-mediated tandem aza-Michael addition-vinylogous nitroaldol condensation has been described between 3,5-dialkyl 4-nitropyrazoles and alkynyl ketones/aldehydes. This transition metal-free atom economical transformation occurred via C-N and C═C bond formations in one step with the elimination of water. The construction of a variety of highly substituted N-fused 3-nitropyrazolopyridine derivatives has been demonstrated with good yields. Good to excellent regioselectivities have been achieved with unsymmetrically substituted 4-nitropyrazoles.