| Abstract
| - Intermolecular Diels−Alder reactions of masked o-benzoquinones, i.e., 6,6-dimethoxy-2,4-cyclohexadienones 5−7 and 21−24 generated from 2-methoxyphenols 1−3 and 17−20, respectively,with electron-deficient dienophiles leading to highly functionalized bicyclo[2.2.2]octenones aredescribed. The masked o-benzoquinones (MOBs) 5−7 underwent Diels−Alder cycloadditions withmethyl acrylate, methyl methacrylate, and methyl vinyl ketone to provide bicyclo[2.2.2]octenones13a−c to 15a−c (direct method) in low to moderate yields with the concomitant formation ofconsiderable amounts of dimers 9−11. To retard dimerization and to improve the yields of therequisite bicyclo[2.2.2]octenones, a detour method comprised of sequential bromination of 2-methoxyphenols 1−4, oxidation and Diels−Alder reaction, and debromination has been developed. Theoxidation of bromophenols 17−20 produced MOBs 21−24 which are stable enough to be isolated.The MOBs 21−24 underwent cycloaddition with electron-deficient dienophiles in a very efficientmanner to afford the corresponding cycloadducts 25a−c to 28a−c in good to high yields withoutself-dimerization. When the cycloadducts 25a−c to 28a−c were treated with either Bu3SnH/AIBNor tributylammonium formate−palladium reagent, the corresponding debrominated products 13a−cto 16a−c were obtained in high to excellent yields. In general, the cycloadducts 13a−c to 15a−cwere obtained in 20−40% higher yields via the detour method than those via the direct method. Inboth routes, the Diels−Alder reactions proceeded in a highly regio- and stereoselective manner tofurnish a single cycloadduct in each case.
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