An efficient and general access to 3, 4-annulated 2-vinylfurans (type II) is provided by the thermally induced ring transformation of epoxyhexenynes (I). Depending on the substitution pattern the reactions proceed either by heating in solution (5a-h) or under short-time thermolysis conditions (61, j). The results are consistent with a multistep mechanism involving 1-oxacyclohepta-3, 4, 6-trienes as central intermediates.
