Intramolecular Diels−Alder Reactions of Brominated Masked o-Benzoquinones. A Detour Method To Synthesize Highly Functionalized Oxatricyclic [m.3.1.0] Ring Systems from 2-Methoxyphenols
| Autor: | Yi-Ling Shen, N. S. Kameswara Rao, Chun-Chen Liao, Ken-Ching Lin |
|---|---|
| Rok vydání: | 2002 |
| Předmět: |
O-Benzoquinones
Intramolecular reaction Chemistry Organic Chemistry Regioselectivity Halogenation Stereoisomerism General Medicine Bridged Bicyclo Compounds Heterocyclic Bromine Ring (chemistry) Medicinal chemistry Chemical synthesis Cycloaddition Adduct Alkaloids Phenols Cascade reaction Intramolecular force Benzoquinones Diels alder Organic chemistry |
| Zdroj: | The Journal of Organic Chemistry. 67:8157-8165 |
| ISSN: | 1520-6904 0022-3263 |
| DOI: | 10.1021/jo020316k |
| Popis: | Intramolecular Diels-Alder (IMDA) reactions of masked o-benzoquinones (MOBs) 5a-d to 7a-d and 17a-d to 19a-d generated in situ from 2-methoxyphenols 2-4 and 14-16, respectively, in the presence of alkenols 1a-d, resulting in highly functionalized oxatricyclic [m.3.1.0] ring systems are described. The MOBs 5a-d to 7a-d underwent the IMDA reactions to furnish the adducts 8a-d, 10a-d, and 12a-d (direct method) in poor yields with the concomitant formation of considerable amounts of unexpected byproducts 9a-d, 11a-d, and 13a-d, respectively. To avoid the formation of byproducts and to improve the yields of the desired cycloadducts, a detour method comprising 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, which underwent cycloaddition to afford the cycloadducts 20a-d to 22a-d, respectively, as sole products in good to high yields in a highly regio- and stereoselective manner. Treatment of the bromoadducts 20a-d to 22a-d with tributylammonium formate-palladium reagent produced the corresponding debrominated products 8a-d, 10a-d, and 12a-d in high to excellent yields. In general, the latter oxatricycles were obtained in higher overall yields via the detour method than those via the direct method. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|