Lewis Acid Promoted Reactions of 11-Methylenepentacyclo2,6.03,10.05,9>undecane-8-one and Pentacyclo2,6.03,10.05,9>undecane-8-one with Ethyl Diazoacetate

Article abstract of DOI:10.1021/jo00298a021

The reaction of pentacyclo<5.4.0^2,6.0^3,10.0^5,9>undecane-8,11-dione (1) with ethyl diazoacetate (EDA, 1 equiv) in the presence of F3B*OEt2, when performed at -78 deg C -> -40 deg C, afforded three products: diethyl 3,6-dioxopentacyclo<6.5.0.0^4,12.0^5,10.0^9,13>tridecane-2,7-dicarboxylate (2, 6.4percent), ethyl 2,6-dioxopentacyclo<5.5.0.0^4,11.0^5,9.0^8,12>dodecane-3-carboxylate (5, 7.4percent), and a novel heterocyclic compound, 7 (31percent), whose structure was established by X-ray structural analysis.Further reaction of 5 with excess EDA in the presence of F3B*OEt2 at +10 deg C -> 25 deg C produced diethyl 2,6-dioxopentacyclo<6.5.0.0^4,12.0^5,10.0^9,13>tridecane-2,6-dicarboxylate (8, 35percent) along with recovered 5 (23percent).The corresponding low-temperature (-78 deg C -> -40 deg C) ring homologation of 11-methylenepentacyclo<5.4.0.0^2,6.0^3,10.0^5,9>undecan-8-one (3) gave two products, 9 and 10.Decarboxylation of the mixture of 9 and 10 yielded a mixture of 11 and 12 (product ratio ca. 15:1).Ozonolysis of this mixture followed by reductive workup afforded two isomeric cage diketones, 13 and 16, in 5.4percent and 90percent yield, respectively.Finally, low-temperature (-78 deg C) ring homologation of pentacyclo<5.4.0.0^2,6.0^3,10.0^5,9>undecan-8-one (4) with EDA (1 equiv)-F3B*OEt2 gave ethyl 3-oxopentacyclo<5.5.0.0^4,11.0^5,9.0^8,12>dodecane-2-carboxylate (17, ca 90percent) along with two unidentified products.Decarboxylation of this product mixture afforded a single cage keton, 18, in 94percent yield.Reduction of 18 with NaBH4-CeCl3 gave the corresponding cage alcohol, 19 (87percent), whose structure was established via X-ray crystallographic analysis of its corresponding 3,5-dinitrobenzoate derivative, 20.