Asymmetric synthesis using diisopropyl tartrate modified (E)- and (Z)-crotylboronates: preparation of the chiral crotylboronates and reactions with achiral aldehydes
作者:William R. Roush、Kaori Ando、Daniel B. Powers、Alan D. Palkowitz、Ronald L. Halterman
DOI:10.1021/ja00173a023
日期:1990.8
Crotylboronates undergo highly diastereo- and enantioselective reactions with aliphatic (linear or α-monobranched; 72-91% ee), aromatic and α,β-unsaturated aldehydes (55-74% ee). The reaction diastereoselectivity closely parallels the reagent isomeric purity especially for reactions performed at −78 o C. The enantioselectivity is best in toluene for all substrates except benzaldehyde where best results
巴豆基硼酸酯与脂肪族(线性或 α-单支链;72-91% ee)、芳香族和 α,β-不饱和醛(55-74% ee)发生高度非对映选择性和对映选择性反应。反应的非对映选择性与试剂异构体纯度密切相关,特别是对于在 -78 o C 下进行的反应。对所有底物的对映选择性在甲苯中最佳,但苯甲醛除外,因为苯甲醛在 THF 中获得最佳结果。本研究中合成的 14 种高烯丙醇中有 9 种的相对和绝对立体化学是通过与 Sharpless 不对称环氧化制备的环氧醇的相关性来确定的
A Study Directed to the Asymmetric Synthesis of the Antineoplastic Macrolide Acutiphycin under Enantioselective Acyclic Stereoselection Based on Chiral Oxazaborolidinone-Promoted Asymmetic Aldol Reactions
作者:Syun-ichi Kiyooka、Mostofa A. Hena
DOI:10.1021/jo990342r
日期:1999.7.1
A shortening of the reaction path can be realized by using a series of the chiral oxazaborolidinone-promoted aldol reaction with respect to the practical synthesis of the (+)-acutiphycin seco acid derivative 5. The linear strategy is based on the utilization of five aldol reactions with a sequence of silyl nucleophiles, 7, 8, 35, 10, and 11, in the presence of stoichiometric amounts of the promoter, 1 or 2. The construction of the relative configuration between the stereogenic centers is diastereoselectively controlled by the stereochemistry of the promoter used in the enantioselective aldol reaction, which is nearly independent of that of the substrate (promoter control).
Silylmethyl radical cyclization: new stereoselective method for 1,3-diol synthesis from allylic alcohols
BCl<sub>3</sub>- and TiCl<sub>4</sub>-Mediated Reductions of β-Hydroxy Ketones
作者:Christopher R. Sarko、Scott E. Collibee、Allison L. Knorr、Marcello DiMare
DOI:10.1021/jo951549x
日期:1996.1.1
Syn-selective reduction protocols for beta-hydroxy ketones are described exploiting the intermediacy of titanium and boron chelates derived from TiCl4 and BCl3, respectively, Reductions are conducted at -78 degrees C in CH2Cl2 using a wide range of CH2Cl2-soluble reducing agents, Added acid-scavenging agents are detrimental to reaction selectivity, An A((1,3))-like interaction involving the stereocenter responsible for asymmetric induction provides conformational biasing of the intermediate chelates necessary for high diastereoselectivity.
DERBALI, Y., J. SOC. CHIM. TUNIS, 2,(1988) N 7, C. 9-16