A Diversity-Oriented Multicomponent Approach to Novel Fused Nitrogen Heterocycles Using 6-Aminoindazole

Abstract

We present a novel, efficient, eco-friendly sonochemical strategy for the synthesis of fused nitrogen heterocycles via Brønsted acid-promoted, one-pot multicomponent reactions (MCRs). This method involves the rapid assembly of 6-aminoindazole, aryl aldehydes, and 1,3-cyclodione derivatives (barbituric acid, dimedone, and 1,3-dimethyl barbituric acid) under mild and identical reaction conditions. The approach delivers a diverse range of highly functionalized heterocyclic frameworks, including 11-phenyl-1,6,7,11-tetrahydro-8H-pyrazolo[3,4-f]pyrimido[4,5-b]quinoline-8,10(9H)-dione, 8,8-dimethyl-11-phenyl-1,6,7,8,9,11-hexahydro-10H-pyrazolo[3,4-a]acridin-10-one, and 7,9-diphenyl-1,6,7,9-tetrahydro-2′H-spiro[pyrazolo[3,4-f]quinoline-8,5′-pyrimidine]-2′,4′,6′(1′H,3′H)-trione derivatives. The molecular structures of these compounds were unambiguously confirmed through 1H-NMR, 13C-NMR and single-crystal X-ray diffraction (SC-XRD) analysis. Additionally, control experiments provided valuable mechanistic insights into the reaction pathway. This protocol stands out for its efficiency, high yields, and broad functional group tolerance, making it a versatile tool for diversity-oriented synthesis in modern heterocyclic chemistry.