A Visible-Light-Triggered & Rhodamine-B Catalyzed Eco-friendly Synthesis of Benzopyrano[2,3-c]pyrazoles

I2-promoted formal [3 + 1 + 1 + 1] cyclization to construct 5-cyano-1H-pyrazolo[3,4-b]pyridine using malononitrile as a C1 synthon

“…3,4 For example, spirooxindole-pyran derivatives and benzopyrano[2,3- c ]pyrazole derivatives were reported by Zhang's group and Jagdamba Singh's group, respectively, using malononitrile as a C2 synthon and C3 synthon under the promotion of visible light, respectively. 5 In recent years, it has also been reported that malononitrile participates in cyclization reactions as a C1 synthon under base- or transition metal-catalyzed reaction conditions for the construction of gem-dicyano compounds [Scheme 2A(a)]. 6 In addition, dehydrocyanation has also been widely reported as an important strategy in organic synthesis; 7 however, to the best of our knowledge, the use of malononitrile as the C1 synthon to construct mono-cyano heterocyclic compounds has rarely been reported [Scheme 2A(d)], possibly because of several challenges associated with this process.…”