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首页> 外文期刊>Chemistry: A European journal >Bulky Monodentate Phosphoramidites in Palladium-Catalyzed Allylic Alkylation Reactions:Aspects of Regioselectivity and Enantioselectivity
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Bulky Monodentate Phosphoramidites in Palladium-Catalyzed Allylic Alkylation Reactions:Aspects of Regioselectivity and Enantioselectivity

机译：钯催化的烯丙基烷基化反应中的大单齿亚磷酰胺：区域选择性和对映选择性方面。

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A series of bulky monoden-tate phosphoramidite ligands,based on biphenol,BINOL and TADDOL backbones,have been employed in the Pd-catalysed allylic alkylation reaction.Reaction of disodium diethyl 2-methyl malonate with monosubstituted allylic substrates in the presence of palladium complexes of the phosphoramidite ligands proceeds smoothly at room temperature.The regioselectivities observed depend strongly on the leaving group and the geometry of the allylic starting compounds.Mono-coordination occurs when these ligands are li-gated in [Pd(allyl)(X)] complexes(allyl = C_3H_5,1-CH_3C_3H_4,1-C_6H_5C_3H_4,1,3-(QH_5)_2C_3H_3;X = C1,OAc).The solid-state structure determined by X-ray diffraction of [Pd(C_3H_5)(l)(Cl)] reveals a non-symmetric coordination of the allyl moiety,caused by the stronger trans influence of the phosphoramidite ligand relative to X".In all of these complexes,the syn,trans isomer is the major species present in solution.Because of fast isomerisation and high reactivity of the syn,cis complex,the major product formed upon alkylation is the linear product,especially for monosubstituted phenylallyl substrates in the presence of halide counterions.In the case of biphenol-and BINOL-based phosphoramidites,however,a strong memory effect is observed when l-phenyl-2-propenyl acetate is employed as the substrate.In this case,nucleophilic attack competes effectively with the isomerisation of the transient cmnamylpalladium complexes.The asymmetric allylic alkylation of 1,3-di-phenyl-2-propenyl acetate afforded the chiral product in up to 93% ee.Substrates with smaller substituents gave lower enantioselectivities.The observed stereoselectivity is explained in terms of a preferential rotation mechanism,in which the product is formed by attack on one of the isomers of the intermediate [Pdjl,3-(C_6H_5)_2C_3H_3)(L)-(OAc)] complex.
机译：Pd催化的烯丙基烷基化反应中使用了一系列基于双酚，BINOL和TADDOL主链的庞大的单齿亚磷酰胺配体.2-甲基丙二酸二乙酯二钠与单取代的烯丙基底物的反应在Pd钯络合物的存在下亚磷酰胺配体在室温下平稳进行。观察到的区域选择性在很大程度上取决于离去基团和烯丙基起始化合物的几何形状。当这些配体连接在[Pd（allyl）（X）]配合物中时发生单配位反应（烯丙基= C_3H_5,1-CH_3C_3H_4,1-C_6H_5C_3H_4,1,3-（QH_5）_2C_3H_3; X = C1，OAc）。通过[Pd（C_3H_5）（l）（Cl）的X射线衍射确定的固态结构）]揭示了烯丙基部分的不对称配位，这是由于亚磷酰胺配体相对于X“的较强反式影响。在所有这些配合物中，顺式，反式异构体是溶液中存在的主要物质。异构化和高反应活性顺式，顺式配合物的烷基化反应的主要产物是线性产物，特别是在卤化物抗衡离子存在下单取代的苯基烯丙基底物。但是，在基于双酚和BINOL的亚磷酰胺的情况下，观察到强烈的记忆效应当以1-苯基-2-丙烯基乙酸乙烯酯为底物时，亲核攻击与瞬态cmnamyl钯配合物的异构化有效竞争。提供1,3-二苯基-2-丙烯基乙酸乙烯酯的不对称烯丙基烷基化取代基较小的底物给出较低的对映选择性。观察到的立体选择性是根据优先旋转机理解释的，其中该产物是通过攻击中间体[Pdjl， 3-（C_6H_5）_2C_3H_3）（L）-（OAc）]复数。

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