pTSA-catalyzed synthesis of functionalized chromeno[2,3-d]pyrimidine/chromeno[4,3-b]chromene derivatives via one-pot three component reaction: mechanistic insights and variable temperature NMR studies to investigate restricted bond rotation

In this study, an efficient and convenient three-component cyclization protocol is presented for the development of synthetically important chromeno[2,3-d]pyrimidine/chromeno[4,3-b]chromene derivatives via pTSA-catalyzed reaction of substituted salicylaldehyde, 1,3-dimethylbarbituric acid/4-hydroxycoumarin, and electron-rich arenes at 80 °C in the presence of ethanol. In addition, variable temperature (VT) ¹H &¹³C NMR spectroscopy is used to study the dynamic Csp²–Csp³ bond between the electron-rich aryl group and the benzylic sp³-carbon. Furthermore, our development is simple and economical, tolerates many functional groups, works with a wide variety of substrates, produces exceptional yields, does not require column chromatography, and allows for scalable synthesis—all of which support the basic principles of green chemistry.