| Abstract
| - Intramolecular Diels−Alder (IMDA) reactions of masked o-benzoquinones (MOBs) 5a−d to 7a−dand 17a−d to 19a−d generated in situ from 2-methoxyphenols 2−4 and 14−16, respectively, inthe presence of alkenols 1a−d, resulting in highly functionalized oxatricyclic [m.3.1.0] ring systemsare described. The MOBs 5a−d to 7a−d underwent the IMDA reactions to furnish the adducts8a−d, 10a−d, and 12a−d (direct method) in poor yields with the concomitant formation ofconsiderable amounts of unexpected byproducts 9a−d, 11a−d, and 13a−d, respectively. To avoidthe formation of byproducts and to improve the yields of the desired cycloadducts, a detour methodcomprising sequential bromination of 2-methoxyphenols 2−4, tandem oxidative acetalization−Diels−Alder reaction, and debromination has been developed. The oxidation of bromophenols 14−16 in the presence of alkenols 1a−d produced the corresponding MOBs 17a−d to 19a−d, whichunderwent cycloaddition to afford the cycloadducts 20a−d to 22a−d, respectively, as sole productsin good to high yields in a highly regio- and stereoselective manner. Treatment of the bromoadducts20a−d to 22a−d with tributylammonium formate−palladium reagent produced the correspondingdebrominated products 8a−d, 10a−d, and 12a−d in high to excellent yields. In general, the latteroxatricycles were obtained in higher overall yields via the detour method than those via the directmethod.
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