Mechanism and origins of regio- and enantioselectivities in RhI-catalyzed hydrogenative couplings of 1,3-diynes and activated carbonyl partners: intervention of a cumulene intermediate.
Mechanism and origins of regio- and enantioselectivities in RhI-catalyzed hydrogenative couplings of 1,3-diynes and activated carbonyl partners: intervention of a cumulene intermediate.
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DOI：
10.1002/chem.201002741
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发表时间：
2011-03-28
影响因子：
4.3
通讯作者：
Houk, Kendall N.
中科院分区：
文献类型：
--
作者：
Liu, Peng;Krische, Michael J.;Houk, Kendall N.
关键词：
采用密度泛函理论研究了铑催化1,3-二炔与邻位二羰基化合物以H2为还原剂的还原偶联机理。通过RhI结合的二羰基通过七元环状累积烯过渡态与共轭二炔进行1,4-加成的氧化偶联导致线性加合物的唯一形成。二炔 1,4-加成比简单炔烃的 1,2-加成快得多。在氧化偶联过程中，1,2-二羰基化合物以双齿形式与铑结合。研究了该反应的化学选择性、区域选择性和对映选择性，并将其归因于这种独特的 1,4-加成途径。配体和远离形成的 C-C 键的炔取代基的紧密接近控制着区域选择性和对映选择性：偶联发生在空间要求更高的炔末端，这最大限度地减少了与配体的非键相互作用。提出了一种立体化学模型，该模型解释了当使用 (R)-联芳基膦配体时优先形成 (R)-构型偶联产物。
The mechanism of the rhodium-catalyzed reductive coupling of 1,3-diynes and vicinal dicarbonyl compounds employing H2 as reductant was investigated by density functional theory. Oxidative coupling through 1,4-addition of the RhI-bound dicarbonyl to the conjugated diyne via a seven-membered cyclic cumulene transition state leads to exclusive formation of linear adducts. Diyne 1,4-addition is much faster than the 1,2-addition to simple alkynes. The 1,2-dicarbonyl compound is bound to rhodium in a bidentate fashion during the oxidative coupling event. The chemo-, regio-, and enantioselectivities of this reaction were investigated and are attributed to this unique 1,4-addition pathway. The close proximity of the ligand and the alkyne substituent distal to the forming C–C bond controls the regio- and enantioselectivity: coupling occurs at the sterically more demanding alkyne terminus, which minimizes nonbonded interaction with the ligand. A stereochemical model is proposed that accounts for preferential formation of the (R)-configurated coupling product when (R)-biaryl phosphine ligands are used.
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