Minor enantiomer recycling – a strategy to improve enantioselectivity

2016 ◽  
Vol 88 (4) ◽  
pp. 309-316 ◽  
Author(s):  
Christina Moberg

AbstractIn enantioselective reactions, the major, desired enantiomer is commonly obtained along with the minor, undesired enantiomer. By continuous recycling of this undesired enantiomer back to starting material, products with improved enantiomeric purity can be obtained. Such in situ minor enantiomer recycling can be accomplished by coupling the catalytic reaction to an exergonic transformation of a sacrificial reagent. The method has been applied to the synthesis of O-acylated cyanohydrins, which serve as starting materials for a variety of biologically active compounds.

RSC Advances ◽  
2015 ◽  
Vol 5 (83) ◽  
pp. 67909-67943 ◽  
Author(s):  
Alessandro K. Jordão ◽  
Maria D. Vargas ◽  
Angelo C. Pinto ◽  
Fernando de C. da Silva ◽  
Vitor F. Ferreira

Lawsone has been used as the starting material for the synthesis of a variety of biologically active compounds and materials.


2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jian-Qiang Chen ◽  
Xiaodong Tu ◽  
Qi Tang ◽  
Ke Li ◽  
Liang Xu ◽  
...  

AbstractAliphatic esters are essential constituents of biologically active compounds and versatile chemical intermediates for the synthesis of drugs. However, their preparation from readily available olefins remains challenging. Here, we report a strategy to access aliphatic esters from olefins through a photocatalyzed alkoxycarbonylation reaction. Alkyloxalyl chlorides, generated in situ from the corresponding alcohols and oxalyl chloride, are engaged as alkoxycarbonyl radical fragments under photoredox catalysis. This transformation tolerates a broad scope of electron-rich and electron-deficient olefins and provides the corresponding β-chloro esters in good yields. Additionally, a formal β-selective alkene alkoxycarbonylation is developed. Moreover, a variety of oxindole-3-acetates and furoindolines are prepared in good to excellent yields. A more concise formal synthesis of (±)-physovenine is accomplished as well. With these strategies, a wide range of natural-product-derived olefins and alkyloxalyl chlorides are also successfully employed.


2017 ◽  
Vol 23 (6) ◽  
Author(s):  
Manjunath B. Channapur ◽  
Roger G. Hall ◽  
Mukul Lal ◽  
Sitaram Pal ◽  
Ashok S. Shyadligeri

AbstractTrifluoromethyl containing heterocycles are an integral part of many biologically active compounds in the agro and pharmaceutical chemistry. Herein, we report an efficient and concise three-step synthesis of 5-halo-6-trifluoromethylpyridine-3-carbonitriles from a trifluoroacetyl vinylogous enamine starting material. Hydrolysis furnishes the carboxylic acids.


2018 ◽  
Author(s):  
Honggui Lv ◽  
Li-Jun Xiao ◽  
Dongbing Zhao ◽  
Qi-Lin Zhou

Herein, we realized the first linear-selective hydroarylation of unactivated alkenes and styrenes with organoboronic acids by introducing directing groupon alkenes. Our method is highly efficient and scalable, and provides a modular route to assemble structurally diverse alkylarenes, especially for γ-aryl butyric acid derivatives, which have been widely utilized as chemical feedstocks to access multiple marketed drugs, and biologically active compounds.<br>


2020 ◽  
Vol 5 (443) ◽  
pp. 85-91
Author(s):  
Ibrayev M.K., ◽  
◽  
Takibayeva A.T., ◽  
Fazylov S.D., ◽  
Rakhimberlinova Zh.B., ◽  
...  

This article presents studies on the targeted search for new derivatives of azoles, such as benzthiazole, 3,5-dimethylpyrazole, 1,3,4-oxadiazole-2-thione, 1,3,4-thiadiazole. The possibility of combining in one molecule of the azole ring with other cyclic compounds: the alkaloid cytisine, morpholine, furan and some arenes has been studied. To obtain new compounds, the reactions of bromination, acylation, and interaction with isothiocyanates were studied. Optimal synthesis conditions were studied for all reactions. It was found that the reaction of 4-bromo-3,5-dimethylpyrazole with isothiocyanates, in contrast to the previously written derivatives of anilines, takes a longer time and requires heating the reaction mixture. The combination of a pirasol fragment with halide substituents often results in an enhanced therapeutic effect. The synthesized 2-bromine-N-(6-rodanbenzo[d]thiazole-2-yl)acetamide, due to the alkylbromide group, is an important synth in the synthesis of new benzthiazole derivatives. Its derivatives combine in one molecule the rest of rhodanbenzthiazole with alkaloid cytisine and biogenic amine morpholine and are potentially biologically active compounds, since the molecule structure contains several pharmacophoric fragments: benzthiazole and alkaloid (amine) heterocycles, rhodane and urea groups. The mechanism of formation of 1,3,4-oxadiazole-2-tyons from hydrazides under action on them by carbon disulfide was studied and assumed. It was shown that dithiocarbamates in acidic medium decompose with the release of hydrogen sulfide and the formation of highly reactive isothiocyanate group. Then, intra-molecular cyclization occurs, with the formation of end products - 1,3,4-oxadiazole-2-thions. The structures of the synthesized compounds were studied by 1H and 13C NMR spectroscopy. All synthesized substances are potentially biologically active compounds, since they contain several pharmacophore fragments in their structure.


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