远程环外官能团对闭环复分解立体化学的影响并用于Amphidinolide X的全合成
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摘要
Amphidinolide X是一个具有细胞毒性的16元环双内酯化合物。本研究利用闭环复分解(RCM)反应来构筑C12-C13三取代双键而成功地合成了AmphidinolideX及其(12Z)-异构体。
第一章中首先介绍了烯烃复分解催化剂的发展,以及影响RCM反应性、E/Z选择性、特别是构筑三取代双键的诸多因素。随后简述了Amphidinolides家族天然产物的结构以及Fürstner小组用于Amphidinolide X全合成的逆合成化学键断裂的方法,从而提出了本研究中采用的RCM策略。
第二章阐述合成C17位带有羟基的C13-C22四氢呋喃醇片断的结果。该片断为Amphidinolide X和Y共通,可用于经RCM反应来合成这两个大环化合物。C19位含氧取代基的季碳是通过不对称双羟化反应引入的,对映选择性很高。而四氢呋喃环是利用酸催化的烯基取代环氧化合物经5-endo模式开环-环化来构筑。前者中的烯基取代基可进一步用于烷基硼参与的Suzuki-Miyaura偶联反应来导入C13上的烯基碳原子。
第三章给出了合成C1-C12酸片断的路线,在C8位上分别带有R及S构型大体积硅氧保护基。其中的反式甲基高烯丙基醇可分别用手性硼和硅试剂经反式优先的醛的丁烯基化反应来制备。同时我们还优化了微波加热用于选择性脱去α,β-不饱和甲酯的条件,而C6位上的酯基则不受影响。
第四章收录了我们利用RCM生成三取代双键的研究结果。首次发现了C8位上的官能团能够影响RCM反应的立体化学。当用20mol%的Grubbs第二代催化剂用于C8-酮底物的RCM反应,可以85%的收率得到单一的(12Z)-AmphidinolideX。相反,(8R)-二苯基叔丁基硅氧基的底物分别用Grubbs第二代催化剂或相关的亚茚基钌络合物进行RCM反应,均生成Amphidinolide X和(12Z)-异构体的混合物,比例为29∶71,(12Z)-异构体为主。用Grubbs第二代催化剂促进的RCM反应收率为50%,而亚茚基钌络合物参与反应的收率为65%,后者可能通过抑制取代苯乙烯副产物的形成而提高产率。取代苯乙烯副产物常见于Grubbs第二代催化剂促进的多官能团RCM底物的反应。本研究工作提供了一个例子,可以通过C8位上环外远程大体积的二苯基叔丁基硅氧基的影响,有限度地在16元环双内酯骨架中形成(12E)型三取代双键。
论文的最后列有实验步骤,新化合物的表征,引用文献以及原始~1H和~(13)C核磁共振谱。
Amphidinolide X, a 16-membered cytotoxic macrodiolide, and its (12Z)-isomer have been synthesized via ring-closing metathesis (RCM) for assembling the C12-C13 trisubstituted double bond.
Chapter 1 introduces the development of olefin metathesis catalysts, and the factors which influence the reactivity and E/Z selectivity of RCM, especially on the aspect of formation of trisubstituted double bonds. The structures of amphidinolides and the retrosynthetic bond disconnection used in the Furstner's total synthesis of amphidinolide X were briefed. It is followed by the presentation of our RCM strategy tackled under the current thesis research.
Chapter 2 describes the synthesis of the C13-C22 tetrahydrofuran fragment appended with a hydroxy group at C17. It is a common structural subunit applicable for total synthesis of amphidinolide X and Y via the RCM approach. The oxygenated chiral quaternary carbon at C19 was assembled by the asymmetric dihydroxylation in high enantioselectivity and the tetrahydrofuran ring was constructed by an acid-catalyzed 5-endo ring-opening cyclization of the epoxide possessing a vinyl moiety. The latter could be also used to facilitate a B-alkyl Suzuki-Miyaura cross-coupling reaction for the introduction of the C13 olefinic carbon.
Chapter 3 presents the synthesis of the C1-C12 acid fragments possessing an (8R)-and (8S)-TBDPSO group, respectively. The anti-methyl homoallylic alcohol was prepared by anti-selective aldehyde crotylation using the chiral boron and silicon reagents. A modified microwave heating procedure was also established for selective cleavage of the a,β-unsaturated methyl ester in the presence of the C6 ester moiety.
Chapter 4 compiles the results of our studies on RCM toward formation of the trisubstituted double bond. Influence on the stereochemical outcome of the RCM by remote exocyclic groups appended at C8 was observed for the first time. (12Z)-Amphidinolide X was synthesized in 85% isolated yield as the sole isomer from the C8-keto substrate in the presence of 20 mol% of the Grubbs second generation catalyst. In contrast, the (8R)-TBDPSO-substituted substrate afforded a 29:71 mixture of amphidinolide X and (12Z)-isomer in 50% and 65% combined yield, respectively, by using 20 mol% of the Grubbs second generation catalyst and the corresponding indenylidene ruthenium complex. The latter was found to suppress formation of the substituted styrene byproduct associated with use of the benzylidene ruthenium complex. This work represents an example of using a bulky TBDPSO group at the remote exocyclic C8 position to partially facilitate formation of the trisubstituted (12E)-alkene embedded in the 16-membered macrodiolide ring.
The experimental section, characterization of all new compounds, cited references, and copies of original ~1H and ~(13)C NMR spectra are found at the end of the thesis.
第一章中首先介绍了烯烃复分解催化剂的发展,以及影响RCM反应性、E/Z选择性、特别是构筑三取代双键的诸多因素。随后简述了Amphidinolides家族天然产物的结构以及Fürstner小组用于Amphidinolide X全合成的逆合成化学键断裂的方法,从而提出了本研究中采用的RCM策略。
第二章阐述合成C17位带有羟基的C13-C22四氢呋喃醇片断的结果。该片断为Amphidinolide X和Y共通,可用于经RCM反应来合成这两个大环化合物。C19位含氧取代基的季碳是通过不对称双羟化反应引入的,对映选择性很高。而四氢呋喃环是利用酸催化的烯基取代环氧化合物经5-endo模式开环-环化来构筑。前者中的烯基取代基可进一步用于烷基硼参与的Suzuki-Miyaura偶联反应来导入C13上的烯基碳原子。
第三章给出了合成C1-C12酸片断的路线,在C8位上分别带有R及S构型大体积硅氧保护基。其中的反式甲基高烯丙基醇可分别用手性硼和硅试剂经反式优先的醛的丁烯基化反应来制备。同时我们还优化了微波加热用于选择性脱去α,β-不饱和甲酯的条件,而C6位上的酯基则不受影响。
第四章收录了我们利用RCM生成三取代双键的研究结果。首次发现了C8位上的官能团能够影响RCM反应的立体化学。当用20mol%的Grubbs第二代催化剂用于C8-酮底物的RCM反应,可以85%的收率得到单一的(12Z)-AmphidinolideX。相反,(8R)-二苯基叔丁基硅氧基的底物分别用Grubbs第二代催化剂或相关的亚茚基钌络合物进行RCM反应,均生成Amphidinolide X和(12Z)-异构体的混合物,比例为29∶71,(12Z)-异构体为主。用Grubbs第二代催化剂促进的RCM反应收率为50%,而亚茚基钌络合物参与反应的收率为65%,后者可能通过抑制取代苯乙烯副产物的形成而提高产率。取代苯乙烯副产物常见于Grubbs第二代催化剂促进的多官能团RCM底物的反应。本研究工作提供了一个例子,可以通过C8位上环外远程大体积的二苯基叔丁基硅氧基的影响,有限度地在16元环双内酯骨架中形成(12E)型三取代双键。
论文的最后列有实验步骤,新化合物的表征,引用文献以及原始~1H和~(13)C核磁共振谱。
Amphidinolide X, a 16-membered cytotoxic macrodiolide, and its (12Z)-isomer have been synthesized via ring-closing metathesis (RCM) for assembling the C12-C13 trisubstituted double bond.
Chapter 1 introduces the development of olefin metathesis catalysts, and the factors which influence the reactivity and E/Z selectivity of RCM, especially on the aspect of formation of trisubstituted double bonds. The structures of amphidinolides and the retrosynthetic bond disconnection used in the Furstner's total synthesis of amphidinolide X were briefed. It is followed by the presentation of our RCM strategy tackled under the current thesis research.
Chapter 2 describes the synthesis of the C13-C22 tetrahydrofuran fragment appended with a hydroxy group at C17. It is a common structural subunit applicable for total synthesis of amphidinolide X and Y via the RCM approach. The oxygenated chiral quaternary carbon at C19 was assembled by the asymmetric dihydroxylation in high enantioselectivity and the tetrahydrofuran ring was constructed by an acid-catalyzed 5-endo ring-opening cyclization of the epoxide possessing a vinyl moiety. The latter could be also used to facilitate a B-alkyl Suzuki-Miyaura cross-coupling reaction for the introduction of the C13 olefinic carbon.
Chapter 3 presents the synthesis of the C1-C12 acid fragments possessing an (8R)-and (8S)-TBDPSO group, respectively. The anti-methyl homoallylic alcohol was prepared by anti-selective aldehyde crotylation using the chiral boron and silicon reagents. A modified microwave heating procedure was also established for selective cleavage of the a,β-unsaturated methyl ester in the presence of the C6 ester moiety.
Chapter 4 compiles the results of our studies on RCM toward formation of the trisubstituted double bond. Influence on the stereochemical outcome of the RCM by remote exocyclic groups appended at C8 was observed for the first time. (12Z)-Amphidinolide X was synthesized in 85% isolated yield as the sole isomer from the C8-keto substrate in the presence of 20 mol% of the Grubbs second generation catalyst. In contrast, the (8R)-TBDPSO-substituted substrate afforded a 29:71 mixture of amphidinolide X and (12Z)-isomer in 50% and 65% combined yield, respectively, by using 20 mol% of the Grubbs second generation catalyst and the corresponding indenylidene ruthenium complex. The latter was found to suppress formation of the substituted styrene byproduct associated with use of the benzylidene ruthenium complex. This work represents an example of using a bulky TBDPSO group at the remote exocyclic C8 position to partially facilitate formation of the trisubstituted (12E)-alkene embedded in the 16-membered macrodiolide ring.
The experimental section, characterization of all new compounds, cited references, and copies of original ~1H and ~(13)C NMR spectra are found at the end of the thesis.
引文
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