نتایج جستجو برای: brønsted acid

تعداد نتایج: 747867  

Journal: :Organic letters 2014
Alexandre Aillerie Vincent Lemau de Talancé Aurélien Moncomble Till Bousquet Lydie Pélinski

The first enantioselective synthesis of 4-aza-podophyllotoxin derivatives by partial transfer hydrogenation of lactone-fused quinolines was achieved using a chiral Brønsted acid catalyst. This reaction was extended to a large scope of substrates with good yields and enantioselectivities.

Journal: :Organic & biomolecular chemistry 2007
Lutz Ackermann Ludwig T Kaspar Andreas Althammer

Two distinct economical catalysts for intramolecular hydroaminations of electronically unactivated alkenes with basic amines are described, which are based on (a) group 4 metal halides under basic reaction conditions or (b) Brønsted-acid organocatalysts.

Journal: :Chemical communications 2012
Haiyun Xu Xinying Zhang Yan He Shenghai Guo Xuesen Fan

A highly efficient synthesis of diversely substituted 2H-pyran-2-ones and indenes through Brønsted acid promoted tandem reaction of the readily obtainable 3-hydroxyhexa-4,5-allenic esters under extremely mild conditions has been developed.

A mild and efficient method has been developed for the preparation of substituted coumarins from reaction of various phenols with different β-ketoesters via Pechmann condensation in the presence of Brønsted acidic ionic liquid (N-(4-sulfonic acid) butyl triethylammonium hydrogen sulfate) as an effective catalyst under solvent-free conditions. Different phenols reacted with ethyl acetoacetate to...

2013
Wei Fu Xin-Hao Li Hong-Liang Bao Kai-Xue Wang Xiao Wei Yi-Yu Cai Jie-Sheng Chen

The catalytic purification of automobile exhaust gases (CO, NOx and hydrocarbons) is one of the most practiced conversion processes used to lower the emissions and to reduce the air pollution. Nevertheless, the good performance of exhaust gas purification catalysts often requires the high consumption of noble metals such as platinum. Here we report that the Brønsted acid sites on the external s...

Journal: :Organic & biomolecular chemistry 2008
Dhevalapally B Ramachary Y Vijayendar Reddy Mamillapalli Kishor

We have developed a new technology called multi-catalysis for the sequential one-pot synthesis of highly functionalized heterocycles. A practical and novel multi-component aniline-, self- and Brønsted acid-catalyzed selective process for the sequential one-pot synthesis of highly substituted 2-(2-hydroxy-aryl)-cyclopentane-1,3-diones, 3,9-dihydro-2H-cyclopenta[b]chromen-1-ones and 3,3-dimethyl-...

2017
Carlos Palo-Nieto Abhijit Sau Ryan Williams M Carmen Galan

A practical approach for the α-stereoselective synthesis of deoxyglycosides using cooperative Brønsted acid-type organocatalysis has been developed. The method is tolerant of a wide range of glycoside donors and acceptors, and its versatility is exemplified in the one-pot synthesis of a trisaccharide. Mechanistic studies suggest that thiourea-induced acid amplification of the chiral acid via H-...

Journal: :Physical chemistry chemical physics : PCCP 2013
Matthew E Potter Danni Sun Enrica Gianotti Maela Manzoli Robert Raja

The ability to adroitly tailor acid-strength using specifically-engineered bimetallic nanoporous materials has been investigated with a view to exploiting their potential in solid-acid catalysed transformations. Further, it has been demonstrated that through site-specific interactions, extra-framework zinc ions can suitably modify the acidity of Brønsted acid sites, to stimulate diverse catalyt...

2011
Xiaoyue Jiang Weidong Ye Xiaohua Song Wenxin Ma Xuejun Lao Runpu Shen

Ionic liquid with both Lewis and Brønsted acid sites has been synthesized and its catalytic activities for Michael addition were carefully studied. The novel ionic liquid was stable to water and could be used in aqueous solution. The molar ratio of the Lewis and Brønsted acid sites could be adjusted to match different reactions. The results showed that the novel ionic liquid was very efficient ...

2017
Christian Malm Heejae Kim Manfred Wagner Johannes Hunger

Solutions of Brønsted acids with bases in aprotic solvents are not only common model systems to study the fundamentals of proton transfer pathways but are also highly relevant to Brønsted acid catalysis. Despite their importance the light nature of the proton makes characterization of acid-base aggregates challenging. Here, we track such acid-base interactions over a broad range of relative com...

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