A regioselective ring-opening cyclization of spirocyclopropanes with sulfonium ylides afforded 2,3-trans-hexahydrobenzopyran-5-ones in high yields without the formation of any diastereoisomers.
Ring-opening cyclization of cyclohexane-1,3-dione-2-spirocyclopropanes using dimethylsulfoxonium methylide proceeded regioselectively to produce 2,3,4,6,7,8-hexahydro-5H-1-benzopyran-5-ones in good to high yields. The reactions of cycloheptane-and cyclopentane-1,3-dione-2-spirocyclopropanes could construct [7.6]-and [5.6]-fused ring systems. This reaction was also carried out using sulfoxonium ethylide, butylide, and benzylide, resulting in the formation of the corresponding 2,3-trans-disubstituted products in good to high yields, and it was shown that the dimethyl group can act as a dummy substituent. It was found that the 2-and 3-phenyhexahydrobenzopyran-5-ones can be readily converted into 5-hydroxyflavan and 5-hydroxyisoflavan, respectively.
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-1benzofuran-4(2H)-ones in high yields in the presence of trimethylsilyl iodide at room temperature. The EWGsubstituted spirocyclopropanes, in turn, underwent regioselective ring opening followed by cyclization, which gave rise to 2-substituted tetrahydrobenzofuran-4ones when a combination of tetrabutylammonium iodide catalyst and trifluoromethanesulfonic acid was used, whereas calcium iodide afforded the 3-substituted derivatives.
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