Synthesis of tetracyclic indenopyrazolopyrazolones through cascade reactions of aryl azomethine imines with propargyl alcohols

Abstract

Presented herein is a novel and efficient synthesis of synthetically and biologically attractive tetracyclic indenopyrazolopyrazolone derivatives through the cascade reactions of aryl azomethine imines with propargyl alcohols. Mechanistically, the formation of the title products is believed to involve an initial inert C(sp²)–H bond alkenylation followed by the cascade formation of two five-membered rings. To our knowledge, this is the first example in which propargyl alcohol acts as not only an alkenylation coupling partner but also a C2/C1 synthon to form indeno/pyrazolo scaffolds. Notable advantages of this novel protocol include easily accessible and moisture/air-stable substrates, high efficiency and excellent atom-economy. In addition, the cytotoxicity test of selected products against two human cancer cell lines demonstrated their potential for pharmaceutical applications.