Asymmetric Synthesis of P-Stereogenic Phosphinic Amides via Pd(0)-Catalyzed Enantioselective Intramolecular C–H Arylation
摘要:
The palladium-catalyzed enantioselective intramolecular C-H arylation of N-(2-haloaryl)-P,P-diphenylphosphinic amides furnishes P-stereogenic phosphine oxide derivatives in 61-99% yield with 88-97% ee. The catalyst generated in situ from a TADDOL-derived phosphoramide ligand and Pd(dba)(2) is optimum in terms of yield and enantioselectivities.
3‐dioxolane‐4,5‐dimethanol (TADDOL)‐based phosphoramidites has been synthesized and applied in the Ni‐catalyzed cycloisomerization of different dienes. Through the systematic variation of the three structural motifs of the lead structure, that is, the amine moiety, the protecting group, and the aryl substituents, the ligand features could be optimized for the asymmetriccycloisomerization of the model substrate
合成了基于α,α,α,α-四芳基-1,3-二氧戊环-4,5-二甲醇(TADDOL)的亚磷酰胺库,并将其用于Ni催化的不同二烯的环异构化。通过铅结构的三个结构基序(即胺部分,保护基和芳基取代基)的系统变化,可以优化配体特征,以使模型底物二烯丙基丙二酸二乙酯的不对称环异构化。新催化体系的底物范围已扩展到其他二烯丙基底物,包括不对称二烯。总体上具有高达13 500 h -1的极高活性,对五元外亚甲基亚环戊烷的选择性很高,对映选择性高达92% ee 已经实现。
Development, Mechanism, and Scope of the Palladium-Catalyzed Enantioselective Allene Diboration
作者:Heather E. Burks、Shubin Liu、James P. Morken
DOI:10.1021/ja070572k
日期:2007.7.1
In the presence of a chiral phosphoramidite ligand, the palladium-catalyzed diboration of allenes can be executed with high enantioselectivity. This reaction provides high levels of selectivity with a range of aromatic and aliphatic allene substrates. Isotopic-labeling experiments, stereodifferentiating reactions, kinetic analysis, and computational experiments suggest that the catalytic cycle proceeds by a mechanism involving rate-determining oxidative addition of the diboron to Pd followed by transfer of both boron groups to the unsaturated substrate. This transfer reaction most likely occurs by coordination and insertion of the more accessible terminal alkene of the allene substrate, by a mechanism that directly provides the eta(3) pi-allyl complex in a stereospecific, concerted fashion.