Hydroxyl-Directed Intermolecular Ketone-Olefin Couplings Promoted by SmI2
摘要:
SmI2-promoted intermolecular ketone-olefin couplings are facilitated and stereocontrolled by hydroxyl groups incorporated within the starting materials. For example, the SmI2-induced ketone - olefin coupling reactions of alpha-hydroxy ketone 5 with ethyl acrylate, acrylonitrile, ethyl crotonate, and 2(5 H)-furanone proceeded with high stereocontrol to afford the syn-1,2-diol products 6-9 in good yields. Excellent diastereoselectivity was achieved in the reductive couplings of beta-hydroxy aldehyde 21 and erythro-beta-hydroxy ketone 24 with acrylonitrile using SmI2, to produce the anti-1,3-diols 22 and 25 in good yields. The sense of the stereo-selectivity was in full accord with a chelation-control model. In the proposed model, the stereochemistry of the reaction product is explained by assuming that a cyclic ketyl radical is generated during the initial single-electron reduction by SmI2. This radical species results from the chelation of the Sm-III cation, attached to the ketyl radical, with the hydroxyl group.
Highly diastereoselective aldol reaction of α-bromo ketones with aliphaticaldehydes was successfully carried out by using titanium(II) chloride and copper in dichloromethane at low temperature. Similarly, Reformatsky-type reaction of α-bromo thioester with aliphaticaldehydes was promoted under mild conditions to afford β-hydroxy thioesters in good to moderate yields.
Boronenolates were in situ generated smoothly by treating α-iodo ketones with 9-BBN-H, and aldols were produced in highly diastereoselective manner by successive reaction with various aldehydes at low temperature.
Chiral Lewis Acid Catalysis in Aqueous Media. Catalytic Asymmetric Aldol Reactions of Silyl Enol Ethers with Aldehydes in a Protic Solvent Including Water
Chiral copper(II)-catalyzed asymmetric aldol reactions of silyl enol ethers with aldehydes have been successfully carried out in a water-ethanol solution. The use of the protic solvent including wa...
手性铜 (II) 催化的甲硅烷基烯醇醚与醛的不对称羟醛反应已在水-乙醇溶液中成功进行。使用质子溶剂包括水...
Scandium trisdodecylsulfate (STDS). A new type of lewis acid that forms stable dispersion systems with organic substrates in water and accelerates aldol reactions much faster in water than in organic solvents
作者:Shū Kobayashi、Takeshi Wakabayashi
DOI:10.1016/s0040-4039(98)01081-8
日期:1998.7
A newtype of Lewisacid, scandium trisdodecylsulfate (STDS), was prepared. In the presence of a catalytic amount of STDS, aldol reactions of silyl enol ethers with aldehydes proceeded smoothly in water without using any organic solvents. It was proven that stable dispersion systems including the catalyst and organic substrates were formed in water and that catalytic activity in water was much higher
Dimethylsilyl enolates and alpha-dimethylsilyl esters reacted with aldehydes in N,N-dimethyl-formamide without an activator to give aldol adducts in moderate to good yields. Under the same conditions, the corresponding trimethylsilyl derivatives exhibited lower reactivities toward the aldol reaction. (C) 1998 Elsevier Science Ltd. All rights reserved.