Synthesis of indenophenanthridine via a [4+2] annulation strategy: a “turn-off’’ Fe3+ ion sensor, practical application in live cell imaging and reversible acidochromism studies

An efficient protocol has been developed for the synthesis of a novel fluorescent probe, 1,2-disubstituted-indeno[1,2,3-gh]phenanthridine, derived from a series of α-oxo-ketene dithioacetals (OKDTAs) and indenoquinoline under essential conditions via a [4+2] annulation in excellent yield.

Metal-Free Catalyzed Synthesis of Fluorescent Indolizine Derivatives

A mild and high efficient method to prepare indolizines by two-component reaction with the acid as the catalyst was developed. In this reaction, a new ring efficiently formed in one-step reaction. A wide range of substrates could be applied and the desired products were obtained in 8-95% yields under metal-free conditions. Different indolizine derivatives (compounds 3a-3n) were synthesized by general conditions and microwave irradiation conditions, and compound 3a gave the best results with an isolated yield of 95% and 82%, respectively. The structures of synthesized compounds were characterized by spectral analysis, and compound 3m was confirmed by single crystal X-ray analysis. UV-vis absorption and fluorescence properties of these compounds were correlated with substituent groups on indolizine rings.