Diels–Alder reactions with pyridine o-quinodimethanes generated from pyridine sulfolenes

An efficient route has been developed for the synthesis of polysubstituted 6,6-dioxo-6,7-dihydrothieno[3,4-b]pyridines , which serve as excellent precursors for generation of the corresponding pyridine o-quinodimethanes. Following thermal extrusion of sulfur dioxide, these reactive species can be trapped in situ with electron rich, neutral, and electron deficient dienophiles. The regio and stereochemical structure of the resulting adducts was determined by NMR analysis.