A Pummerer-based generation and trapping of furo[3,4-c]pyridines: an approach to nitrogen containing heterocyclic analogues of 1-arylnaphthalene lignans

The Pummerer reaction of o-benzoyl substituted pyridylmethyl sulfoxides generates α-thiocarbocations, the interception of which by the neighbouring keto functionality produces thio-substituted furo[3,4-c]pyridines as transient intermediates; the latter undergo [4+2] cycloaddition with an added dienophile. Base-induced ring opening of the cycloadducts followed by aromatization gives substituted isoquinolines related to heterocyclic analogues of 1-arylnaphthalene lignans.