56 モノテルペノイドイソキノリンおよびインドールアルカロイドの合成

概要

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Both ipecac and corynantheine-heteroyohimbine alkaloids are monoterpenoid alkaloids which are biogenetically derived from secologanin. In view of these structural relationship, we have succeeded in the stereoselective synthesis of both alkaloids by using 2,3-disubstituted benzo- or indoloquinolizidine as a common key intermediate. [Total Synthesis of (±)-Emetine] Reductive photocyclization of two N-furoylenamine types of enamides (2a) and (3) gave two benzoquinolizidines (4a) and (5) having a C_2-unit either at 2- or 3-position. The former (4a) was stereoselectively converted into the key intermediate (12) for the synthesis of (±)-emetine. The dihydro compound (14) of the latter was subjected to retro-Michael followed by Michael reaction with 2-lithioacetamide (26b) and 1-(lithiomethyl)isoquinoline (1c) to give two key intermediates (12) and (29) for another approach to (±)-emetine. [Total Synthesis of (±)-Ajmalicine and (±)-Corynantheine] By the same methodology as above, harmalane (1b) was converted into the acetyllactam (33) which is subjected to chemoselective and stereoselective reductions to afford the acetylester (38) and the δ-lactone (35) which are known to be key intermediates for the synthesis of (±)-ajmalicine and (±)-corynantheine, respectively.
天然有機化合物討論会の論文
1986-09-09