MNBA-Mediated β-Lactone Formation: Mechanistic Studies and Application for the Asymmetric Total Synthesis of Tetrahydrolipstatin
摘要:
Various beta-lactones were prepared from beta-hydroxycarboxylic acids by intramolecular dehydration condensation using MNBA, an effective coupling reagent, along with a nucleophilic catalyst. The transition state that provides the desired 4-membered ring model system is disclosed by density functional theory (DFT) calculations, and the structural features of the transition form are discussed. This method was successfully applied to the asymmetric total synthesis of tetrahydrolipstatin (THL), an antiobestic drug used in clinical treatment to inhibit the activity of pancreatic lipase.
Rhodium‐Catalyzed Parallel Kinetic Resolution of Racemic Internal Allenes Towards Enantiopure Allylic 1,3‐Diketones
作者:Lukas J. Hilpert、Bernhard Breit
DOI:10.1002/anie.201903365
日期:2019.7.15
parallel kinetic resolution of racemic 1,3‐disubstituted allenes by means of a rhodium‐catalyzed addition to 1,3‐diketones furnishing enantiopure allylic 1,3‐diketones is described. Mechanistic experiments demonstrate that the different allene enantiomers react in parallel to either the diastereomeric E‐ or Z‐allylic 1,3‐diketones with the same absoluteconfiguration of the newly formed stereogenic
We report that aromatic propargylation is achievable with secondary propargylic fluorides, thus affording 1-alkyl-1-aryl-2-alkynes. In the present case, hydrogen bonding is responsible for the activation of the C–F bond. A large excess of arene nucleophile is shown to be necessary to achieve good yields.
Ruthenium-catalyzedpropargylicreduction of propargylicalcohols bearing a terminal alkyne moiety is accomplished by using Hantzsch ester as a nucleophilic hydride source. A variety of secondary and tertiary propargylicalcohols are reduced to the corresponding propargylic reduced products such as 1-alkynes in excellent yields. Some mechanistic studies indicate that ruthenium–allenylidene complexes
Stereoselective Synthesis of Monofluoroalkyl α,β-Unsaturated Ketones From Allenyl Carbinol Esters Mediated by Gold and Selectfluor
作者:Zhuang Jin、Rachel S. Hidinger、Bo Xu、Gerald B. Hammond
DOI:10.1021/jo301239p
日期:2012.9.7
Allenyl carbinol ester 3 isomerizes to an E,Z mixture of the corresponding diene 2 in the presence of gold catalyst 4, but the resulting mixture yields monofluoroalkyl α,β-unsaturatedketone 1 with exclusive E selectivity and in high yields after reaction with Selectfluor.
A Simple, Mild and General Oxidation of Alcohols to Aldehydes or Ketones by SO
<sub>2</sub>
F
<sub>2</sub>
/K
<sub>2</sub>
CO
<sub>3</sub>
Using DMSO as Solvent and Oxidant
作者:Gao‐Feng Zha、Wan‐Yin Fang、Jing Leng、Hua‐Li Qin
DOI:10.1002/adsc.201900104
日期:2019.5.14
A practical, general and mild oxidation of primary and secondary alcohols to carbonyl compounds proceeds in yields of up to 99% using SO2F2 as electrophile in DMSO as both the oxidant and the solvent at ambient temperature. No moisture‐ and oxygen‐free conditions are required. Stoichiometric amount of inexpensive K2CO3, which generates easy to separate by‐products, is used as the base. Thus, 5‐gram
在环境温度下,使用SO 2 F 2作为亲电子试剂在DMSO中作为氧化剂和溶剂,伯醇和仲醇进行实用,通用且温和的氧化成羰基化合物的收率可达99%。不需要无湿气和无氧条件。化学计量的廉价K 2 CO 3生成易于分离的副产物的油基用作基础。因此,通过简单的过滤作为后处理,以几乎定量的产量进行了5克规模的运行。还应注意使用通常促进竞争的Pummerer重排的极性溶剂(例如DMSO)。该协议与(杂)芳烃,烯烃和炔烃底物上的各种常见的N-,O-和S-官能团兼容(68个例子)。该方案被应用(99%的产率)用于重要的降胆固醇药物瑞舒伐他汀的正式合成。