(5α,9α,11β)-11-Hydroxy-6,7,8,9-tetrahydro-5H-5,9-propanobenzo[7]annulen-7-one ethylene ketal (6a) and its 11α-methyl derivative (6b) were prepared from monoketal 3. These compounds underwent acid-catalyzed transannular reactions leading to 6,7,8,9-tetrahydro-5H-5,9-propanobenzo[7]annulene derivatives 5a, 8a and 5b, 8b, respectively, depending on the reaction conditions. The compounds 6a and 6b were dehydrated to 6,7,8,9-tetrahydro-5H-5,9-prop[1]enobenzo[7]annulen-7-one (9a) and its 11-methyl derivative (9b), respectively. The conformational analysis of the 5,9-propanobenzo[7]annulene derivatives by molecular mechanics calculations (MM3 program) and the 1H NMR data show that hydroxyketal 6a and the related compound (5α,7β,9α)-6,7,8,9-tetrahydro-5H-5,9-propanobenzo[7]annulen-7-ol (4) exist mainly in the boat-chair conformation with the boat cycloheptenol ring, while for hydroxyketal 6b the chair-boat conformation (chair cycloheptenol ring) seems to be the preferred one.
(5α,9α,11β)-11-羟基-6,7,8,9-四氢-5H-5,9-丙烷基苯并[7]茚-7-酮乙烯缩合物(6a)及其11α-甲基衍生物(6b)是从单酮3制备的。这些化合物经过酸催化的过渡环反应,根据反应条件,生成6,7,8,9-四氢-5H-5,9-丙烷基苯并[7]茚衍生物5a、8a和5b、8b。化合物6a和6b被脱水成6,7,8,9-四氢-5H-5,9-丙烯基苯并[7]茚-7-酮(9a)及其11-甲基衍生物(9b)。通过分子力学计算(MM3程序)和1H NMR数据对5,9-丙烷基苯并[7]茚衍生物进行构象分析,结果表明羟基缩酮6a及其相关化合物(5α,7β,9α)-6,7,8,9-四氢-5H-5,9-丙烷基苯并[7]茚-7-醇(4)主要存在于带有舟型-椅型构象的舟型环庚烯醇环中,而羟基缩酮6b则偏向于椅型-舟型构象(椅型环庚烯醇环)。