Asymmetric Michael additions to .alpha.,.beta.-unsaturated oxazolines. An efficient preparation of chiral .beta.,.beta.-disubstituted propionaldehydes
摘要:
A short stereoselective route to a variety of chiral, nonracemic alpha,beta-unsaturated oxazolines derived from (S)-tert-leucinol is described. Addition of organolithium reagents to this chiral oxazoline occurs in a Michael fashion, giving rise to adducts with high diastereoselectivity. Reductive cleavage of the oxazoline leaves the beta,beta-disubstituted aldehydes in > 93% ee. This process represents a significant improvement in one of the earliest asymmetric conjugate additions first reported in 1975.
Herein we report the palladium-catalyzed isomerization of highly substituted allylic alcohols and alkenyl alcohols by means of a single catalytic system. The operationally simple reaction protocol is applicable to a broad range of substrates and displays a wide functional group tolerance, and the products are usually isolated in high chemical yield. Experimental and computational mechanistic investigations
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
A General Organocatalytic System for Enantioselective Radical Conjugate Additions to Enals
作者:Emilien Le Saux、Dengke Ma、Pablo Bonilla、Catherine M. Holden、Danilo Lustosa、Paolo Melchiorre
DOI:10.1002/anie.202014876
日期:2021.3
enantioselective conjugate addition of carbon‐centered radicals to aliphatic and aromatic enals. The process uses an organic photoredox catalyst, which absorbs blue light to generate radicalsfrom stable precursors, in combination with a chiral amine catalyst, which secures a consistently high level of stereoselectivity. The generality of this catalytic platform is demonstrated by the stereoselective interception
The direct introduction of sp3 carbon fragments at the β position of α,β-unsaturated aldehydes is greatly complicated by competing 1,2-addition manifolds. Previous catalytic enantioselective conjugate addition methods, based on the use of organometallic reagents or ground-state iminium ion activation, could not provide general and efficient solutions. We report herein that, by turning them into strong
isomerization of primary allylic alcohols to chiral aldehydes using iridium‐catalysts bearing P,N‐MaxPHOX ligands has been studied. These catalysts can be fine‐tuned as they present three different stereogenic centers to modulate both the reactivity and enantioselectivity of a family of different substrates. The experimental part is supported by a DFT study of the reaction mechanism, which provides new