improved generation of chiral cationic iridium catalysts for the asymmetricisomerization of primaryallylicalcohols is disclosed. The design of these air‐stable complexes relied on the preliminary mechanistic information available, and on Charton analyses using two preceding generations of iridium catalysts developed for this highly challenging transformation. Sterically unbiased chiral aldehydes
Copper(<scp>i</scp>)-catalysed asymmetric allylic reductions with hydrosilanes
作者:T. N. Thanh Nguyen、Niklas O. Thiel、Johannes F. Teichert
DOI:10.1039/c7cc07008j
日期:——
copper(I)-catalysed asymmetric allylic reduction enables a regio- and stereoselective transfer of a hydride nucleophile in an SN2′-fashion onto allylic bromides. This transformation represents a conceptually orthogonal approach to allylic substitution reactions with carbon nucleophiles. A copper(I) complex based upon a chiral N-heterocyclic carbene (NHC) ligand allows for stereoselectivity reaching 99% ee
铜(I)催化的不对称烯丙基还原可实现S N 2'形式的氢化物亲核试剂的区域和立体选择性转移到烯丙基溴上。这种转变代表了与碳亲核试剂进行烯丙基取代反应的概念上正交的方法。基于手性N-杂环卡宾(NHC)配体的铜(I)配合物可使立体选择性达到99%ee。不管起始材料的双键构型如何,该催化剂都能进行立体收敛反应。
Enantioselective iminium-catalyzed epoxidation of hindered trisubstituted allylic alcohols
作者:Roman Novikov、Jérôme Lacour
DOI:10.1016/j.tetasy.2010.06.002
日期:2010.6
The reactivity of diastereomeric biaryl iminium cations made of a (Ra)-5,5',6,6',7,7',8,8'-octahydrobinaphthyl core and exocyclic appendages derived from (S)- or (R)-3,3-dimethylbutyl-2-amine was investigated with hindered trisubstituted allylic alcohols a class of alkenes which had not been previously studied in detail in epoxidation reactions with cyclic iminium catalysts (ee up to 98%). Surprisingly, generally strong matched/mismatched effects are observed not only in terms of reactivity but also on the enantioselectivity of the reaction (Ace up to 16%). Also, for the most hindered substrates, two sets of reaction conditions were tested in a preliminary study and little advantage was found in running reactions in MeCN/water instead of CH(2)Cl(2)/water/18-C-6. In any case, the presence of the hydroxyl group did not reveal any anchimeric effect. (C) 2010 Elsevier Ltd. All rights reserved.