Cycloaddition Across the Benzofuran Ring as an Approach to the Morphine Alkaloids
作者:Stefan France、Jutatip Boonsombat、Carolyn A. Leverett、Albert Padwa
DOI:10.1021/jo8016956
日期:2008.10.17
The intramolecular Diels-Alder reaction of several amidofurans tethered onto a benzofuran ring was examined as a strategy for the synthesis of morphine. Bromo substitution on the furan ring did not provide sufficient activation to allow the cycloaddition to take place across the aromatic benzofuran. However, the presence of a large o-methylbenzyl group on the amido nitrogen atom causes the reactive s-trans conformation of the amidofuran to be highly populated, thereby facilitating its Diels-Alder cycloaddition across a tethered benzofuran.
Intramolecular Cyclization Reactions of 5-Halo- and 5-Nitro-Substituted Furans
作者:Kenneth R. Crawford、Scott K. Bur、Christopher S. Straub、Albert Padwa
DOI:10.1021/ol035233k
日期:2003.9.1
[GRAPHICS]Intramolecular cyclization reactions of 5-halo- and 5-nitro-substituted furanylamides were examined. The 2-alkoxy-5-bromofuran derivative 2 produced the rearranged dihydroquinone 6 (36%), a product from the rearrangement of the intermediate oxabicycle 3. The 5-halo substituted furoyl amide 18 was converted to the polyfunctional oxabicycle 20 in 82% yield and at a much faster rate than the unsubstituted furanyl system 17. The 5-nitro-substituted furfuryl amide 33b underwent an unusual isomerization-cyclization reaction under microwave conditions to provide 1,4-dihydro-2H-benzo[4,5]furo[2,3-c]pyridin-3-one 34.