Diastereoselectivity of Additions to Chiral Carbonyl Oxides
摘要:
The influence of a resident stereocenter on the formation of hydroperoxy acetals from carbonyl oxides is investigated. Addition of either methanol or 2-propanol to 8-phenylpropanal O-oxide proceeds with modest stereoselectivity; addition of a tertiary alcohol proceeds with higher selectivity. Product stereochemistry, which is confirmed by conversion of a functionalized hydroperoxy acetal to a 1,2-dioxane, is found to derive from nucleophilic attack through a Felkin-Anh type transition state. Trapping of a carbonyl oxide containing a neighboring hydrogen bond donor proceeds with modest selectivity for both syn- and anti-carbonyl oxide isomers. Ozonolysis of a 3-(trialkylstannyl)-1-enol ether proceeds with loss of the stannyl-bearing carbon through the possible intermediacy of a vinyl peroxide.
Saegusa Oxidation of Enol Ethers at Extremely Low Pd-Catalyst Loadings under Ligand-free and Aqueous Conditions: Insight into the Pd(II)/Cu(II)-Catalyst System
作者:Quan Zhu、Yunsong Luo、Yongyan Guo、Yushun Zhang、Yunhai Tao
DOI:10.1021/acs.joc.0c02987
日期:2021.4.16
system of Saegusa oxidation, which converts enolethers to the corresponding enals with a number of diverse substrates at extremely low catalyst loadings (500 mol ppm) under ligand-free and aqueous conditions, is described. Its synthetic utility was demonstrated by large-scale applications of the catalyst system to important nature molecules. This work allows Saegusa oxidation to become a highly practical
The reaction of dialkyl acetals derived from α,β-unsaturated aldehydes with Grignard reagents using TiCl4in THF afforded the cross coupling products, allyl ethers, in high yields. The TiCl4-promotedreaction of alkyl 2,4-dichlorophenyl acetals, synthesized from 3,4-dihydro-2H-pyran or ethyl vinyl ether and 2,4-dichlorophenol, with Grignard reagents in THF at low temperature afforded the corresponding
Highly <i>E</i>-Selective, Stereoconvergent Nickel-Catalyzed Suzuki–Miyaura Cross-Coupling of Alkenyl Ethers
作者:Guo-Ming Ho、Heiko Sommer、Ilan Marek
DOI:10.1021/acs.orglett.9b00946
日期:2019.4.19
An improved method for the nickel-catalyzed Suzuki-Miyaura cross-coupling of alkenyl ethers is reported. This stereoconvergent protocol allows for the utilization of a wide range of alkenyl ethers and aryl boronic esters for the synthesis of variously substituted styrene derivatives. An olefinic mixture with respect to the alkenyl ethers can be employed, thereby circumventing the stereodefined synthesis of starting materials. Preliminary mechanistic investigations indicate a nickel-catalyzed olefin isomerization following initial stereoretentive cross-coupling.