Synthesis of enantiomerically pure bicyclo[4.2.0] octanes by Cu-catalyzed [2+2] photocycloaddition and enantiotopos-differentiating ring opening
Synthesis of enantiomerically pure bicyclo[4.2.0] octanes by Cu-catalyzed [2+2] photocycloaddition and enantiotopos-differentiating ring opening
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DOI：
10.1002/anie.200600946
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发表时间：
2006-01-01
影响因子：
16.6
通讯作者：
Bach, Thorsten
中科院分区：
文献类型：
--
作者：
Braun, Ingbert;Rudroff, Florian;Bach, Thorsten
通过开链1，7-二烯的Cu催化的分子内[2+ 2]光环加成反应[5]的替代方法是不可行的。当我们尝试底物1和2的[2+ 2]光环化加成反应时，没有迹象表明形成所需的双环[4.2]。0]辛烷值显然，Cu催化的光环加成反应需要两个双键与金属原子的配位，[6]这仅适用于与1，6-二烯的反应，导致双环[3.2]。0]我们现在提出了一种逆合成概念（方案1），其包括底物如C（Z= CO）的对映异构体区分开环反应，用于合成对映异构体纯的双环[4.2. 0]辛烷，由结构B表示。因为三环化合物C涵盖双环[4.2. 0]辛烷和双环[3.2. 0]庚烷结构，它应该可以通过Cu催化的二烯D的[2+ 2]光环加成反应获得。在这里，我们报告的成功应用这一概念的一个具体的例子。我们设想对映体选择性Baeyer-Villiger氧化作为对映体区分反应，[7]因此需要羰基作为官能团Z（方案1，C，Z= CO）。1，3-二乙烯基-2-环戊酮的不稳定性及其不期望的光化学反应（α-裂解，氧杂-二-对-甲烷重排）促使我们以保护形式引入羰基（Z= CHOTBDMS，TBDMS=叔丁基二甲基甲硅烷基）。因此，我们尝试了用容易获得的[8]二烯3进行Cu催化的[2+ 2]光环化加成反应（方案2）。的
The alternative approach by Cu-catalyzed, intramolecular [2+ 2] photocycloaddition reactions [5] of open-chain 1, 7-dienes is not viable. When we attempted [2+ 2] photocycloaddition reactions of substrates 1 and 2, there was no indication for the formation of the desired bicyclo [4.2. 0] octane. Apparently Cu-catalyzed photocycloaddition reactions require the coordination of both double bonds to the metal atom,[6] which is feasible only for reactions with 1, 6-dienes leading to bicyclo [3.2. 0] heptanes.We now propose a retrosynthetic concept (Scheme 1) that encompasses an enantiotopos-differentiating ring-opening reaction of substrates such as C (Z= CO) for the synthesis of enantiomerically pure bicyclo [4.2. 0] octanes, represented by structure B. Because tricyclic compound C encompasses both bicyclo [4.2. 0] octane and bicyclo [3.2. 0] heptane structures, it should be accessible by Cu-catalyzed [2+ 2] photocycloaddition reaction of diene D. Herein, we report the successful application of this concept to a specific example. We envisioned an enantioselective Baeyer–Villiger oxidation as the enantiotopos-differentiating reaction,[7] which thus requires a carbonyl group as the functional group Z (Scheme 1, C, Z= CO). The instability of a 1, 3-divinyl-2-cyclopentanone and its undesired photochemical reactions (a-cleavage, oxa-di-p-methane rearrangement) prompted us to incorporate the carbonyl group in protected form (Z= CHOTBDMS, TBDMS= tert-butyldimethylsilyl). Accordingly, we attempted a Cu-catalyzed [2+ 2] photocycloaddition reaction with the readily available [8] diene 3 (Scheme 2). The