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[摘要]：Using an intramolecular [4 + 2] cycloaddition/rearrangement cascade of 3-(1,4-dioxaspiro[4,4]non-7-en-7-yl)-N-furan-2-ylpropionamide (23) as the key step, the BCD core of the lycopodium alkaloid fawcettidine was constructed. Heating the initially formed Diels-Alder cycloadduct at 180 degrees C results in a nitrogen-assisted ring opening followed by a deprotonation/reprotonation of the ensuing zwitterion to give a rearranged hexahydroindolinone. Our attempts to induce a related intramolecular furan Diels-Alder reaction (IMDAF) from the corresponding ketone of 23 failed to give any cycloaddition product. Instead, the only product obtained corresponded to a cyclopentenone derivative derived by isomerization of the double bond into the thermodynamically more stable alpha,beta-position. Efforts toward construction of the final skeleton of fawcettidine by ring A closure of the rearranged cycloadduct derived from furanyl amide 23 are discussed. |
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