Stereodefined Acyclic Polysubstituted Silyl Ketene Aminals: Asymmetric Formation of Aldol Products with Quaternary Carbon Stereocenters

2015 ◽  
Vol 54 (48) ◽  
pp. 14393-14397 ◽  
Author(s):  
Zackaria Nairoukh ◽  
Ilan Marek
Keyword(s):  
Quaternary Carbon ◽  
Ketene Aminals

Bleaching ability of pre-hydrolyzed pulps in the context of a biorefinery mill

TAPPI Journal ◽  
2013 ◽  
Vol 12 (11) ◽  
pp. 49-53 ◽  
Author(s):  
CHRISTINE CHIRAT ◽  
LUCIE BOIRON ◽  
DOMINIQUE LACHENAL
Keyword(s):  
Carbon Content ◽  
Acid Hydrolysis ◽  
13C Nmr ◽  
Kraft Lignin ◽  
Kappa Number ◽  
Hydroxyl Groups ◽  
Kraft Pulps ◽  
Quaternary Carbon ◽  
Oxygen Delignification

Autohydrolysis and acid hydrolysis treatments were applied on mixed softwood chips. The cooking ability was studied by varying the alkali and duration of the cook. Pulps with kappa numbers varying from 30 to 70 were obtained. The bleaching ability of these pulps was studied and compared to control kraft pulps. The prehydrolyzed pulps were shown to be more efficiently delignified by oxygen than the control kraft pulps starting from the same kappa number. Furthermore, the final bleaching was also easier for these pulps. It was also shown that extensive oxygen delignification applied on high-kappa pre-hydrolyzed pulps could be a way to improve the overall yield, which is a prerequisite for the development of such biorefinery concepts. Lignin was isolated from the control kraft and the two pre-hydrolyzed kraft pulps and analyzed by 13C NMR. Lignins from pre-hydrolyzed kraft pulps had similar free phenolic groups content to the control kraft lignin, but their aliphatic hydroxyl groups and β-O-4 content were lower than for the control lignin. The quaternary carbon content was the same for all the samples.

Three-Component [1+1+1] Cyclopropanation with Ruthenium(II)

2018 ◽  
Author(s):  
Tanner C. Jankins ◽  
Robert R. Fayzullin ◽  
Eugene Khaskin
Keyword(s):  
Quaternary Carbon ◽  
Poor Control ◽  
One Step ◽  
Synthetic Routes ◽  
Mechanistic Investigations ◽  
Chiral Centers ◽  
Metal Catalyzed ◽  
The Right ◽  
Substituted Cyclopropanes

We report a one-step, Ru(II)-catalyzed cyclopropanation reaction that is conceptually different from the previously reported protocols that include Corey-Chaykovsky, Simmons-Smith, and metal catalyzed carbene attack on olefins. Under the current protocol, various alcohols are transformed into sulfone substituted cyclopropanes with excellent isolated yields and diastereoselectivities. This new reaction forms highly congested cyclopropane products with three new C–C bonds, three or two new chiral centers and one new quaternary carbon center. 22 examples of isolated substrates are given. Previously reported synthetic routes for similar substrates are all multi-step, linear routes that proceed with overall low yields and poor control of stereochemistry. Experimental mechanistic investigations suggest initial metal-catalyzed dehydrogenation of the alcohol substrate and catalyst independent stepwise attack of two equivalents of sulfone on the aldehyde under basic conditions. While the Ru(II) is only responsible for the initial dehydrogenation step, the rate of aldehyde formation is crucial to maintaining the right balance of intermediates needed to afford the cyclopropane product.

Quaternary Carbon Center Forming [3 + 2] Cyclization Reaction by Adjusting the Substituents of Substrates

2019 ◽  
Vol 84 (21) ◽  
pp. 13871-13880 ◽  
Author(s):  
Xie-Chao Yang ◽  
Jin-Yu Liu ◽  
Zhen Liu ◽  
Xiu-Qin Hu ◽  
Peng-Fei Xu
Keyword(s):  
Cyclization Reaction ◽  
Quaternary Carbon

Remote Stereocontrolled Construction of Vicinal Axially Chiral Tetrasubstituted Allenes and Heteroatom-Functionalized Quaternary Carbon Stereocenters

2019 ◽  
Vol 21 (2) ◽  
pp. 503-507 ◽  
Author(s):  
Pei Zhang ◽  
Qiuhong Huang ◽  
Yuyu Cheng ◽  
Rongshi Li ◽  
Pengfei Li ◽  
...  
Keyword(s):  
Quaternary Carbon ◽  
Axially Chiral

Oxidative Alkylation/Alkynylation of Terminal Alkenes via Alkylaldehyde Decarbonylation and 1,2-Alkynyl Migration

2021 ◽  
Author(s):  
Jiajia Zhang ◽  
De Chen ◽  
yiqun qin ◽  
Wei Deng ◽  
Yongyue luo ◽  
...  
Keyword(s):  
Functional Group ◽  
Quaternary Carbon ◽  
Metal Free ◽  
Terminal Alkenes ◽  
Oxidative Alkylation

A metal-free oxidative alkene alkylation/alkynylation of 1,4-enyn-3-ols with alkylaldehydes has been achieved, which offers a general access to the challenging quaternary carbon-containing but-3-yn-1-ones. The method features with excellent functional group...

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