Asymmetric Allylic Substitution Catalyzed byC1-Symmetrical Complexes of Molybdenum: Structural Requirements of the Ligand and the Stereochemical Course of the Reaction
作者:Andrei V. Malkov、Laure Gouriou、Guy C. Lloyd-Jones、Ivo Starý、Vratislav Langer、Paul Spoor、Victoria Vinader、Pavel Kočovský
DOI:10.1002/chem.200501574
日期:2006.9.6
Application of new chiral ligands (R)-(-)-12 a and (S)-(+)-12 c (VALDY), derived from amino acids, to the title reaction, involving cinnamyl (linear) and isocinnamyl (branched) type substrates (4 and 5 --> 6), led to excellent regio- and enantioselectivities (>30:1, < or =98 % ee), showing that ligands with a single chiral center are capable of high asymmetric induction. The structural requirements
衍生自氨基酸的新手性配体(R)-(-)-12 a和(S)-(+)-12 c(VALDY)在标题反应中的应用,涉及肉桂基(线性)和异肉桂基(支化)型底物(4和5-> 6)导致极佳的区域选择性和对映体选择性(> 30:1,<或= 98%ee),表明具有单个手性中心的配体能够进行高度不对称诱导。讨论了配体的结构要求和机理。氘标记底物的单一对映体(线性38 c和支链37 c)的应用以及通过(2)H (1)H} NMR光谱法在手性液晶基质中分析产物(41-43)区分反应的立体化学途径。对于配体(S)-(+)-12 c,匹配的支链底物对映体为(S)-5,通过涉及立体化学净保留的过程将其转化为具有很高的区域和立体选择性的(R)-6。发现支链底物的错配对映异构体为(R)-5,其也被转化为(R)-6,即具有明显的净反转,但是速率较低且总对映选择性较低。可以称为“记忆效应”的后一个特征降低了外消旋底物(+/