5-Isopropyl-2H-cyclohepta[b]furan-2-one (1) reacted with DMSD to give dimethyl(5-isopropyl-2-oxo-2H-cyclohepta[b]furan-3-yl)sulfonium trifluoromethanesulfonate (2), which was treated with E(t)3N to give 5-isopropyl-3-methylthio-2H-cyclohepta[b]furan-2-one (3). Sulfide 3 was oxidized with mCPBA to give sulfoxide 4 and sulfone 5. The salt 6 which comes from the treatment of 4 with Tf2O converted to an unexpected product, 5,5'-diisopropyl-3,3'-bi-2H-cyclohepta[b]furan-2-one (7), thermally.
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Morita et al. (2007) studied this question.
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