Abstract
The dehydrogenation reaction of a mixture of heptalene-1,2- and heptalene-4,5-dimethanols 4a and 4b with basic MnO2 in AcOEt at room temperature led to the formation of the corresponding heptaleno[1,2-c]furan-1-one 6a and heptaleno[1,2-c]furan-3-one 7a (Scheme 2). Both products can be isolated by chromatography on silica gel. The methylenation of the furan-3-one 7a with 1 mol-equiv. of Tebbe's reagent at −25 to −30° afforded the 2-isopropenyl-5-methylheptalene-1-methanol 9a, instead of the expected 3,6-dimethylheptaleno[1,2-c]furan 8 (Scheme 3). Also, the treatment of 7a with Takai's reagent did not lead to the formation of 8. On standing in solution at room temperature, or more rapidly on heating at 60°, heptalene 9a undergoes a reversible double-bond shift (DBS) to 9b with an equilibrium ratio of 1 : 1.
Jin, X