A facile and robust approach for synthesis and structural characterization of an unprecedented ring system of 4H-pyrazolo[3,4-f]indolizine-4,9(2H)-dione derivatives

Abstract

A facile and efficient route for the synthesis of novel 4H-pyrazolo [3,4-f]indolizine-4,9(2H)-dione derivatives was investigated and confirmed as a robust method. 2-Acetyl pyrrole was reacted with dimethylformamide dimethyl acetal (DMF-DMA) to afford the enaminone, (3-(dimethylamino)-1-(1H-pyrrol-2-yl)prop-2-en-1-one). The latter obtained enaminone was treated with C-ethoxycarbonyl-N-arylhydrazonoyl chloride derivatives in mild reaction conditions to give unprecedented 4H-pyrazolo [3,4-f]indolizine-4,9(2H)-dione derivatives. The structures of novel pyrazolo-indolizine derivatives were confirmed by NMR spectra, mass spectrometry, elemental analyses, as well as single-crystal X-ray diffraction. Also, 4H-pyrazolo [3,4-f]indolizine-4,9(2H)-dione derivatives were confirmed chemically via the reaction of enaminone with C-methoxycarbonyl-N-arylhydrazonoyl chlorides. By this protocol, a wide range of pyrazolo-indolizine-4,9-dione with different substitutions could be prepared in a straightforward manner under mild reaction conditions in good to excellent yields.