Synthesis and Oxidative Cyclization of 3-(1-Cycloalkenyl)tropolones

Abstract
3-(1-Cyclopentenyl)-, 3-(1-cyclohexenyl)-, and 3-(1-cycloheptenyl)tropolones (3a, 3b, and 3c) were prepared by the hydrolysis of cycloadducts of dichloroketene to cyclopentylidene-, cyclohexylidene-, and cycloheptylidenecyclopentadiene, respectively. Compound 3a was oxidized with performic acid to give 1,2,3,5-tetrahydrocyclohepta[b]cyclopenta[d]furan-5-one and 3-(2-oxocyclopentyl)tropolone. Oxidation of 3b and 3c gave 1,2,3,4-tetrahydro-6H-cyclohepta[b]benzofuran-6-one (4b) and 5,7,8,9,10,11-hexahydrodicyclohepta[b,d]furan-5-one, respectively. Dehydrogenation of 4b with palladium catalyst gave 6H-cyclohepta[b]benzofuran-6-one.