Functionalised pyridine sulfolenes as precursors to pyridine o-quinodimethane derivatives and their [4+2] cycloadducts

An efficient route has been developed for the synthesis of polysubstituted 6,6-dioxo-6,7-dihydrothieno[3,4-b]pyridine 5. This pyridine sulfolene compound serves as an excellent precursor for the corresponding pyridine o-quinodimethane. This reactive species is generated via thermal extrusion of sulfur dioxide and can be trapped in situ with both electron-rich and electron-deficient dienophiles.