1,3-Dihydro-2,2-dioxothieno[3,4-c]pyridines as precursors for pyridine o-quinodimethane systems

Various pyridine o-quinodimethane systems were generated via thermal extrusion of sulfur dioxide from 1,3-dihydro-2,2-dioxothieno[3,4-c]pyridine precursors and derivatives functionalised in the 1- or 3-position of the sulfolene ring moiety. Depending on the nature of the peri-substituents on the pyridine ring either the E- or Z-isomers are formed, which react further via inter- and intramolecular Diels–Alder reactions or via an 1,5-H shift, respectively.