Iodide-Catalyzed Ring-Opening Cyclization of Cyclohexane-1,3-dione-2-spirocyclopropanes

The ring-opening cyclization of 2',3'-nonsubstituted and 2'-electron-withdrawing group (EWG)-substituted cyclohexane-1,3-dione-2-spirocyclopropanes was accomplished using iodide as a catalyst. The nonsubstituted derivatives afforded 3,5,6,7-tetrahydro-1-benzofuran-4(2H)-ones in high yields in the presence of trimethylsilyl iodide at room temperature. The EWG-substituted spirocyclopropanes, in turn, underwent regioselective ring opening followed by cyclization, which gave rise to 2-substituted tetrahydrobenzofuran-4-ones when a combination of tetrabutylammonium iodide catalyst and trifluoromethanesulfonic acid was used, whereas calcium iodide afforded the 3-substituted derivatives.