Ir-catalysed allylic substitution: mechanistic aspects and asymmetric synthesis with phosphorus amidites as ligands
作者:Björn Bartels、Günter Helmchen
DOI:10.1039/a900864k
日期:——
Ir-catalysed allylic alkylations of enantiomerically enriched monosubstituted allylic acetates proceed with up to 79% retention of configuration using P(OPh)3 as ligand; further evidence supports the assumption of σ-allyl complexes as intermediates, and high regio- and enantioselectivity in asymmetric allylic alkylations of achiral or racemic substrates is achieved with phosphorus amidites as ligands.
Ir-catalysed allylicalkylations of enantiomerically enriched monosubstituted allylic acetates proceed with up to 87% retention of configuration using P(OPh)3 as ligand. High regio- and enantioselectivity of up to 86% ee in asymmetric allylicalkylations of achiral or racemic substrates is achieved with monodentate phosphorus amidites as ligands. Lithium N-tosylbenzylamide was identified as a suitable
使用 P(OPh)3 作为配体,Ir 催化的烯丙基烷基化对映体富集的单取代烯丙基乙酸酯的构型保留率高达 87%。以单齿磷酰胺作为配体,在非手性或外消旋底物的不对称烯丙基烷基化中实现了高达 86% ee 的高区域和对映选择性。N-tosylbenzylamide 锂被确定为适合烯丙基胺化的亲核试剂。特别重要的是使用氯化锂作为添加剂,通常会导致对映选择性增加。通过 X 射线晶体结构分析和光谱数据对两种 (π-烯丙基) IrIII 配合物进行了表征。
Allyl 4-Chlorophenyl Sulfone as a Versatile 1,1-Synthon for Sequential α-Alkylation/Cobalt-Catalyzed Allylic Substitution
rare 1,1-dipole synthons, allyl sulfones are rarely used in target-oriented syntheses, likely due to the lack of a general catalytic method for their branch-selective allylicsubstitution. Herein, we identified allyl 4-chlorophenyl sulfone as a versatile linchpin for both base-mediated α-derivatization and subsequent cobalt-catalyzed allylicsubstitution. The sequential transformations allow for highly
An Ir-catalyzed asymmetric allylic alkylation using chiral diaminophosphine oxide is described. Asymmetric allylic alkylation of terminal allylic carbonates proceeded using 5 mol % of Ir catalyst, 5 mol % of DIAPHOX 1i, 10 mol % of NaPF6, 10 mol % of LiOAc, and N,O-bis(trimethylsilyl)acetamide (BSA), affording the corresponding branched products in excellent yield and in up to 95% ee. The developed
Iridium-Catalyzed Kinetic Asymmetric Transformations of Racemic Allylic Benzoates
作者:Levi M. Stanley、Chen Bai、Mitsuhiro Ueda、John F. Hartwig
DOI:10.1021/ja103779e
日期:2010.7.7
Versatile methods for iridium-catalyzed, kinetic asymmetric substitution of racemic, branched allylic esters are reported. These reactions occur with a variety of aliphatic, aryl, and heteroaryl allylic benzoates to form the corresponding allylic substitution products in high yields (74-96%) with good to excellent enantioselectivity (84-98% ee) with a scope that encompasses a range of anionic carbon and heteroatom nucleophiles. These kinetic asymmetric processes occur with distinct stereochemical courses for racemic aliphatic and aromatic allylic benzoates, and the high reactivity of branched allylic benzoates enables enantioselective allylic substitutions that are slow or poorly selective with linear allylic electrophiles.