Enantioselective Diels-Alder Reactions of Unsaturated β-Ketoesters Catalyzed by Chiral Ruthenium PNNP Complexes.
Enantioselective Diels-Alder Reactions of Unsaturated β-Ketoesters Catalyzed by Chiral Ruthenium PNNP Complexes.
复制标题
手性钌 PNNP 配合物催化不饱和 β-酮酯的对映选择性 Diels-Alder 反应。
DOI：
10.2533/chimia.2011.231
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发表时间：
2011
期刊：
影响因子：
1.2
通讯作者：
A. Mezzetti
中科院分区：
文献类型：
--
作者：
C. Schotes;A. Mezzetti
我们报道了阳离子Ru PNNP络合物，它促进了α-亚甲基-β-酮酯与各种双烯的不对称Diels-Alder反应。由[RuCl2，(PNNP)]和(Et3O)PF6(2当量)原位生成的配合物[Ru(OEt2)2(PNNP)](PF6)2催化这种不饱和的β-酮酯的Diels-Alder反应，得到了新的烷氧基羰基四氢-1-吲哚衍生物(9例)，ee高达93%。底物-催化剂加合物的晶体结构表明，底物的下表面被PNNP配体的苯环遮蔽，这解释了高的对映选择性。二烯从不饱和的β-酮酯的开放对映体表面的攻击与产物的绝对构型一致。这种方法的一个有用的应用是与戴恩氏二烯反应得到雌酮衍生物，其ee高达99%，酯-外/内比高达145：1(重结晶后)。除了全碳四元中心的不对称形成外，这种方法值得注意，因为不饱和的β-酮酯很少用于Diels-Alder反应。此外，对映体纯雌酮衍生物由于其潜在的应用而引起人们的兴趣，包括治疗乳腺癌。
We report here dicationic ruthenium PNNP complexes that promote the enantioselective Diels-Alder reaction of alpha-methylene beta-ketoesters with various dienes. Complex [Ru(OEt2)2(PNNP)](PF6)2, formed in situ from [RuCl2,(PNNP)] and (Et3O)PF6 (2 equiv.), catalyzes the Diels-Alder reaction of such unsaturated beta-ketoesters to give novel alkoxycarbonyltetrahydro-1-indanone derivatives (nine examples) with up to 93% ee. The crystal structure of the substrate-catalyst adduct shows that the lower face of the substrate is shielded by a phenyl ring of the PNNP ligand, which accounts for the high enantioselectivity. The attack of the diene from the open re enantioface of the unsaturated beta-ketoester is consistent with the absolute configuration of the product. A useful application of this method is the reaction with Dane's diene to give estrone derivatives with up to 99% ee and an ester-exo:endo ratio of up to 145:1 (after recrystallization). Besides the enantioselective formation of all-carbon quaternary centers, this methodology is notable because unsaturated beta-ketoesters have been rarely used in Diels-Alder reactions. Furthermore, enantiomerically pure estrone derivatives are interesting in view of their potential applications, including the treatment of breast cancer.