TOTAL SYNTHESIS OF CARPANONE
TOTAL SYNTHESIS OF CARPANONE
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DOI：
10.1021/ja00753a073
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发表时间：
1971-01-01
影响因子：
15
通讯作者：
CLARDY, JC
中科院分区：
文献类型：
--
作者：
CHAPMAN, OL;ENGEL, MR;CLARDY, JC
Carpanone(1)，一种从Carpano树皮中获得的木脂素，2构成了一个重要的合成挑战。该分子不具有对称性，有五个相邻的不对称中心。在分析问题时，人们可以想象由烯醇醚单元对邻苯二酸亚甲基(2)进行亲核攻击而形成的苯并二恶环。这种方法具有特别的吸引力，因为它可能与角叉酮的生物合成有关。2所需的前驱体2具有C2对称轴，该对称轴穿过连接两个邻苯二胺单元的键的中点，但既没有中心也没有对称面。合成活性物种，如双邻苯并亚甲基(2)是一项艰巨的任务，但巴顿对松萝卜酸3的出色合成表明，酚偶联可能成功。在这种做法中，必须面对两个问题。首先，偶联必须发生在苯乙烯基双键上，而不是芳环上，其次，偶联过程形成两个不对称中心，这两个中心必须具有正确的立体化学。实际上，立体化学问题比乍看起来要困难得多，因为所有中心的立体化学都是在第一键的形成过程中决定的。合成了所需的2-(IRA)-4，5-亚甲二氧基苯酚(3，MP87-88).
Carpanone (1), a lignan obtained from the bark of the carpano tree, 2 poses a significant synthetic challenge. The molecule possesses no element of symmetry and has five contiguous asymmetric centers. In analyzing the problem, one can imagine the benzodioxane ring to be formed by nucleophilic attack of an enol ether unit on an o-quinonemethide (2). This approach has particular appeal because it may be related to the biosynthesis of carpanone. 2 The required precursor 2 has a C2 axis of symmetry which passes through the midpoint of the bond joining the two o-quinonemethide units but has neither a center nor a plane of symmetry. Synthesis of a reactive species such as the bis-o-quinonemethide (2) is a formidable task, but Barton’s brilliant synthesis of usnic acid3 suggests that phenolic coupling might succeed. Two problems must be faced in this approach. First, coupling must occur on the styryl double bond rather than the aromatic ring, and, second, the coupling process forms two asymmetric centers which must have the correct stereochemistry. Actually, the stereochemi-cal problem is more difficult than it first appears be-cause the stereochemistry at all centers is determined in the formation of the first bond. The required 2-(ira «il-propenyl)-4, 5-methylenedi-oxyphenol (3, mp 87-88) was prepared from 2-allyl-