Enantioselective reductive coupling of 1,3-enynes to heterocyclic aromatic aldehydes and ketones via rhodium-catalyzed asymmetric hydrogenation: Mechanistic insight into the role of Bronsted acid additives
Enantioselective reductive coupling of 1,3-enynes to heterocyclic aromatic aldehydes and ketones via rhodium-catalyzed asymmetric hydrogenation: Mechanistic insight into the role of Bronsted acid additives
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DOI：
10.1021/ja0673027
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发表时间：
2006-12-27
影响因子：
15
通讯作者：
Krische, Michael J.
中科院分区：
文献类型：
--
作者：
Komanduri, Venukrishnan;Krische, Michael J.
在杂环芳香醛和酮的存在下，使用手性改性的阳离子铑预催化剂对1，3-烯炔1a-进行加氢，导致还原偶联，得到具有出色水平的区域和对映体控制的二烯基化α-羟基杂芳烃2 - 23。在衍生自BINOL的手性Akiyama− Terada型磷酸作为布朗斯台德酸助催化剂的存在下，使用非手性铑催化剂偶联烯炔与2-吡啶甲醛，得到具有显著光学富集水平（82%ee）的偶联产物2。这一结果表明，底物质子化和/或形成强氢键发生在立体C-C键形成事件之前。此外，高水平的不对称诱导表明醛与布朗斯特酸的相互作用激活了系统的C-C偶联。在元素氘气氛下，烯炔1a和2-吡啶甲醛的还原偶联提供了单氘代产物氘-2，这与涉及炔-羰基氧化偶联随后氢解裂解所得草胺金属内酯的催化机理一致。偶联产物的二烯侧链发生了不同的选择性转化，偶联产物2和8分别转化为化合物24 - 26和27 - 29。
Hydrogenation of 1,3-enynes1a−ein the presence of heterocyclic aromatic aldehydes and ketones using chirally modified cationic rhodium precatalysts results in reductive coupling to afford dienylated α-hydroxy heteroarenes2−23with exceptional levels of regio- and enantiocontrol. Coupling of enyne1ato 2-pyridinecarboxaldehyde using an achiral rhodium catalyst in the presence of a chiral Akiyama−Terada-type phosphoric acid derived from BINOL as the Brønsted acid co-catalyst provides the coupling product2with substantial levels of optical enrichment (82% ee). This result suggests that substrate protonation and/or formation of a strong hydrogen bond occurs in advance of the stereogenic C−C bond forming event. Further, the high levels of asymmetric induction demonstrate that interaction of the aldehyde with the Brønsted acid activates the system toward C−C coupling. Reductive coupling of enyne1aand 2-pyridinecarboxaldehyde under an atmosphere of elemental deuterium provides the monodeuterated productdeuterio-2, consistent with a catalytic mechanism involving alkyne−carbonyl oxidative coupling followed by hydrogenolytic cleavage of the resulting oxametallacycle. The diene side chain of the coupling products is subject to diverse selective transformations, as demonstrated by the conversion of coupling products2and8to compounds24−26and27−29, respectively.