Regioselective opening of epoxy alcohols: mild chemo- and stereoselective preparation of iodohydrins and 1,2-diols
摘要:
Several 2,3-epoxy alcohols have been opened, at -60-degrees-C, with MgI2, leading to the corresponding 3-iodo 1,2-diols with a high level of regio- and chemoselectivity. The iodohydrins can be reduced "in situ", by means of nBu3SnH, to the corresponding 1,2-diols. The chemo-, regio-, and stereocontrol of the reaction makes the method of wide use. Furthermore, epoxy alcohol derivatives (acetyl, benzyl, or TBMS) still maintain a strong preference for C-3 attack of the nucleophile. The experimental data strongly suggest that a metal (Mg) centered chelate is formed throughout the reaction, which gives rise to the regioselective delivery of the iodide ion.
Electrochemical Deprotection of <i>para</i>-Methoxybenzyl Ethers in a Flow Electrolysis Cell
作者:Robert A. Green、Katherine E. Jolley、Azzam A. M. Al-Hadedi、Derek Pletcher、David C. Harrowven、Oscar De Frutos、Carlos Mateos、David J. Klauber、Juan A. Rincón、Richard C. D. Brown
DOI:10.1021/acs.orglett.7b00641
日期:2017.4.21
undivided electrochemical flow reactor in MeOH solution, leading to the unmasked alcohol and p-methoxybenzaldehyde dimethylacetal as a byproduct. The electrochemical method removes the need for chemical oxidants, and added electrolyte (BF4NEt4) can be recovered and reused. The method was applied to 17 substrates with high conversions in a single pass, yields up to 92%, and up to 7.5 g h–1 productivity. The
对-甲氧基苄基(PMB)醚的电化学脱保护是在未分开的电化学流动反应器中的MeOH溶液中进行的,从而产生未掩蔽的醇和对甲氧基苯甲醛二甲基乙缩醛的副产物。电化学方法消除了对化学氧化剂的需求,并且可以回收和再利用添加的电解质(BF 4 NEt 4)。该方法一次通过即可应用于高转化率的17种基材,产率高达92%,生产率高达7.5 gh –1。在一些其他常见的醇保护基的存在下,也选择性地除去了PMB保护基。
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‐Heterocyclic Carbene‐Catalyzed Enantioselective Intramolecular Annulations to Construct Benzo‐Fused Pyranones with Quaternary Stereocenter
作者:Krzysztof Dzieszkowski、Zbigniew Rafiński
DOI:10.1002/adsc.202000550
日期:2020.9.21
intramolecular NHC‐catalyzed approach for the synthesis of benzo‐fused pyranones bearing quaternary stereocenter is described. The developed methodology is based on annulation reaction between acyl anion intermediates and β,β‐disubstituted Michael acceptors. The reaction offers streamlined and effective access to target products in a highly stereoselective manner.