Synthesis of pyrazolidinone fused cinnolines via the cascade reactions of 1-phenylpyrazolidinones with vinylene carbonate

Presented herein is an efficient synthesis of pyrazolidinone fused cinnolines through the cascade reactions of 1-phenylpyrazolidinones with vinylene carbonate. The reaction is initiated by C–H bond cleavage followed by C–C/C–N bonds formation and double C–O bonds cleavage. To our knowledge, this is the first example in which pyrazolidinone fused cinnoline derivatives free of redundant substituents were prepared by using vinylene carbonate as an operationally secure and commercially available ethylene equivalent. Moreover, this synthetic method is suitable for scale-up scenarios with reduced loading of catalyst and additive, and the products thus obtained can be conveniently derived to furnish other kinds of valuable products. Compared with literature methods, this new protocol has advantages such as easily accessible substrates with broad scope, good compatibility with diverse functional groups, concise synthetic procedure, external oxidant free, use of catalytic amount of additive, high efficiency and sustainability.