具緯環式並列平行雙鍵的化合物 40 經七步反應後， 可得具苯硒羰氧基的緯環式化合物 47， 總產率為 29 %。 四環化合物 40 首先進行酯化反應可得乙醯基化合物 41。 隨後乙醯基化合物 41 在甲苯中加熱脫去一氧化碳， 可得到環內1,3-環己二烯的結構， 然後與苯?進行 Diels-Alder 反應而得環己烯二酮化合物 42。 將環己烯二酮化合物 42 還原成環己烯二醇化合物 43， 然後進行芳香族化可得具稠合苯環之化合物 44。 還原反應所得之化合物 45 與 1,1’-羰化二咪?反應可得化合物 46， 接著與苯硒醇進行親核性加成消去反應得到自由基反應之前趨物 47。 化合物 47 與三丁基錫氫及三乙基硼烷在甲苯中進行分子內自由基環化反應後， 可得到具 γ-內酯結構的U 型跨環化合物 48。 化合物 48 為兩次 5-exo-trig 親電性環合反應後的產物。 利用二維核磁共振光譜完成具 γ-內酯結構的化合物 48 之結構式鑑定。 與具並列平行雙鍵之緯環式化合物和溴進行跨環加成反應相比較， 化合物 47 進行分子內自由基環化反應時具有較高的位置選擇性。 Selenocarbonate 47 was synthesized from tetracyclic compound 40 which containing face-proximate double bonds located in the laticyclic topology in seven steps with a total yield of 29 %. Tetracyclic compound 40 was converted to acetate 41 by esterification. Decarbonylation of acetate 41 in refluxing toluene afforded the endocyclic 1,3-cyclohexadiene moiety, which subsequently reacted with p-benzoquinone to furnish the Diels-Alder adduct 42. Reduction of cyclohexendione 42 gave the corresponding cyclohexendiol 43 in good yield. Then, cyclohexenediol 43 was subjected to aromatization affording the benzo-fused tetracyclic acetate 44. Alcohol 45 was obtained from reduction of 44 followed by reaction with 1,1’-carbonyldiimidazole to give imidazoyl carbamate 46. Nucleophilic addition-elimination of 46 with benzeneselenol provided the desired compound 47. Radical cyclization of 47 was carried out by reaction with tributyltin hydride and triethylborane in toluene solution to give U-type transannular carbon-carbon bond formation of γ-lactone 48. Structural identification of 48 was supported by 2-D NMR analysis. In comparison with bromination on the paralleled face to face ethylene bridges of polycyclic hydrocarbons, intramolecularly transannular cyclization via radical intermediate of our case gives more regioselectivity.
