6-Substituted Bicyclohept-5-en-2-one Ketals

Article abstract of DOI:10.1021/jo00272a033

Structurally specific syntheses of isomerically pure 6-substituted bicyclo<2.2.1>hept-5-en-2-one ketals were explored.A conversion of the Diels-Alder adduct of itaconic anhydride with cyclopenta-1,3-diene into a ketal of 6-methylbicyclo<2.2.1>hept-5-en-2-one was accomplished, but the last step, an oxidative vicinal bisdecarboxylation, gave only a 35percent yield.The ethylene ketal of 6-methylbicyclo<2.2.1>hept-5-en-2-one was prepared in 80percent overall yield from bicyclo<2.2.1>hept-5-en-2-one by a regioselective replacement of hydrogen with a methyl group.Practical synthesesof the 6-bromo, 6-carbomethoxy, 6-phenylthio, and 6-trimethylsilyl analogues were accomplished similarly.