Atropisomeric amides as chiral ligands: Using (-)-sparteine-directed enantioselective silylation to control the conformation of a stereogenic axis
Atropisomeric amides as chiral ligands: Using (-)-sparteine-directed enantioselective silylation to control the conformation of a stereogenic axis
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DOI：
10.1021/jo0007074
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发表时间：
2000-10-20
影响因子：
3.6
通讯作者：
Helliwell, M
中科院分区：
文献类型：
--
作者：
Clayden, J;Johnson, P;Helliwell, M
一个对映体纯的(1-三甲基硅基)乙基，由(-)-雀花碱定向的对映体选择性猝灭侧化的叔胺基芳香胺构成，对相邻叔胺取代基的构象施加了强大的热力学控制。6位上的酰胺的邻位石化和官能化使得单一的酰胺构象可以被捕获为对映异构体和非对映异构体纯的酰胺阿托品。酰胺的原脱硅反应得到了具有单一绝对构型的立体轴的官能化阿托品异构体，其外消旋的障碍已经用旋光法确定。含膦取代基的对映体纯酰胺是钯催化的烯丙基取代反应中的有效配体-首次使用非联芳基阿托品作为手性配体-并得到90%ee的产物。钯的存在对膦取代酰胺的消旋速率有很大的影响。
An enantiomerically pure (1-trimethylsilyl)ethyl group, constructed by a (-)-sparteine-directed enantioselective quench of a laterally lithiated tertiary aromatic amide, exerts powerful thermodynamic control over the conformation of the adjacent tertiary amide substituent. Ortholithiation and functionalization of the amide in the 6-position allows the single amide conformer to be trapped as an enantiomerically and diastereoisomerically pure amide atropisomer. Protodesilylation of the amide gives functionalized atropisomeric amides with a stereogenic axis of single absolute configuration, whose barriers to racemization have been determined by polarimetry. Enantiomerically pure amides bearing phosphine substituents are effective ligands in a Pd-catalyzed allylic substitution reaction-the first use of a nonbiaryl atropisomer as a chiral ligand-and give products with 90% ee. The rate of racemization of the phosphine-substituted amide is powerfully influenced by the presence of palladium.