scholarly journals Cyclic Ether Triggers for Polymeric Frustrated Lewis Pair Gels

2021 ◽  
Author(s):  
Utku Yolsal ◽  
Thomas A. R. Horton ◽  
Meng Wang ◽  
Michael P. Shaver
Keyword(s):  
Cyclic Ether ◽  
Frustrated Lewis Pair

Participation of 19-ester groups in the cleavage of 2α,3α- and 5α,6α-steroid epoxides. A case of competition between participation and external nucleophile attack

1979 ◽  
Vol 44 (5) ◽  
pp. 1496-1509 ◽  
Author(s):  
Pavel Kočovský ◽  
Václav Černý
Keyword(s):  
Perchloric Acid ◽  
Hydrobromic Acid ◽  
Ester Group ◽  
Carbonyl Oxygen ◽  
Cyclic Carbonate ◽  
Cyclic Ether ◽  
Normal Reaction ◽  
Neighboring Group ◽  
Ether Oxygen ◽  
The Difference

Acid cleavage of the acetoxy epoxide IIIa with aqueous perchloric acid or hydrobromic acid gave two types of products, i.e. the diol Va or the bromohydrin VIa, and the cyclic ether VIII. The latter compound arises by participation of ether oxygen of the ester group. On reaction with perchloric acid the epoxide IVa gave the diol XIIIa as a product of a normal reaction and the isomeric diol Xa as a product arising by intramolecular participation of the carbonyl oxygen of the 19-acetoxy group. Participation of the 19-ester group is confirmed by the formation of the cyclic carbonate XI when the 19-carbonate IVb is treated analogously. On reaction with hydrobromic acid, the epoxide IVa gave solely the bromohydrin XIVa as a product of the normal reaction course. Discussed is the similarity of these reactions with electrophilic additions to the related 19-acetoxy olefins I and II, the mechanism, the difference in behavior of both epoxides III and IV, the dependence of the product ratio on the nucleophility of the attacking species, and the competition between participation of an ambident neighboring group and an external nucleophile attack.

Participation of 19-substituents in electrophilic additions to 6,7-unsaturated 5α-cholestane and B-homo 5α-cholestane derivatives; A case of competition between the participation of an ambident neighboring group and external nucleophile attack

1980 ◽  
Vol 45 (2) ◽  
pp. 559-583 ◽  
Author(s):  
Pavel Kočovský ◽  
Ladislav Kohout ◽  
Václav Černý
Keyword(s):  
Perchloric Acid ◽  
Hydrobromic Acid ◽  
Cyclic Ether ◽  
Cyclic Ethers ◽  
Neighboring Group ◽  
Acid Cleavage ◽  
Neighbouring Group Participation ◽  
Aqueous Perchloric Acid ◽  
The Difference ◽  
Electrophilic Additions

Hypobromous acid action upon the 6,7-unsaturated 19-substituted 5α-cholestans Va-Vc results in the formation of two types of products, the cyclic ethers IX as products of 5(O)n participation of the 19-substituent, and the bromohydrins X. All these compounds are formed from the 6α,7α-bromonium ions Va'-Vc'. Under the same conditions the B-homo-5α-cholestane derivatives VIIa-VIIc afforded solely the cyclic ethers XIV as products of 5(O)n participation of the 19-substituent in the cleavage of the bromonium ions VIIa'-VIIc'. Acid cleavage of the 6α,7α-epoxides VIb and VIc with aqueous perchloric acid or hydrobromic acid gave two types of products, i.e. the cyclic ethers XI and the diols XII or bromohydrines XIII. The cyclic ethers XI arise by 5(O)n participation of the 19-substituent. The B-homo-6α, 7α-epoxide VIIIc on cleavage with aqueous perchloric acid have solely the cyclic ether XVc and by treatment with hydrobromic acid VIIIc afforded the mixture of XVc, as the main product, and of the bromohydrin XVIc. Discussed is the similarity of the bromonium ion cleavage with the fission of the corresponding epoxides, the mechanism of these reactions and the difference in the behaviour of the isomeric olefins Ia-c, IIIa-c, Va-c and VIIa-c and epoxides IIb,c, IVb,c, VIb,c and VIIIb,c. The competition between ambident neighbouring group participation and external nucleophile attack is discussed as well as the dependence of the products ratio on the nucleophilicity of the attacking species.

Mechanism of acid cleavage of some steroid epoxides. Competition between neighboring group participation and external nucleophile attack

1982 ◽  
Vol 47 (1) ◽  
pp. 124-129 ◽  
Author(s):  
Pavel Kočovský ◽  
František Tureček ◽  
Václav Černý
Keyword(s):  
Perchloric Acid ◽  
Cyclic Ether ◽  
Oxirane Ring ◽  
Neighboring Group ◽  
Group Participation ◽  
Acid Cleavage ◽  
Neighboring Group Participation

The mechanism of perchloric acid cleavage of epoxides I and II was established on the basis of experiments using H2 18O. The 2α,3α-epoxide I gave two products: the cyclic ether V (60%) arising by 5(O)n participation of the 19-acetoxyl and the diol VI (40%). The latter compound is formed by two mechanisms: 1) By direct cleavage of the oxirane ring with H2 18O as external nucleophile and 2) by 7(O)π,n participation via the ion III. Under the same conditions the 5α,6α-epoxide II yielded two diols: The diequatorial diol VIII (96%) arising by 6(O)π,n participation and the diaxial diol IX which is again formed by both direct cleavage of the oxirane ring with H2 18O and by 7(O)π,n participation via the intermediate ion X. The competition of several mechanisms is discussed.

scholarly journals Generation of highly amenable cellulose-Iβ via selective delignification of rice straw using a reusable cyclic ether-assisted deep eutectic solvent system

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Chiranjeevi Thulluri ◽  
Ravi Balasubramaniam ◽  
Harshad Ravindra Velankar
Keyword(s):  
Enzymatic Hydrolysis ◽  
Rice Straw ◽  
Deep Eutectic Solvent ◽  
Solvent System ◽  
Cyclic Ether ◽  
Cellulolytic Enzymes ◽  
Ammonium Bromide ◽  
Selective Delignification ◽  
Cellulose Iβ ◽  
Hydrolysis Of

AbstractCellulolytic enzymes can readily access the cellulosic component of lignocellulosic biomass after the removal of lignin during biomass pretreatment. The enzymatic hydrolysis of cellulose is necessary for generating monomeric sugars, which are then fermented into ethanol. In our study, a combination of a deep eutectic (DE) mixture (of 2-aminoethanol and tetra-n-butyl ammonium bromide) and a cyclic ether (tetrahydrofuran) was used for selective delignification of rice straw (RS) under mild conditions (100 °C). Pretreatment with DE-THF solvent system caused ~ 46% delignification whereas cellulose (~ 91%) and hemicellulose (~ 67%) recoveries remained higher. The new solvent system could be reused upto 10 subsequent cycles with the same effectivity. Interestingly, the DE-THF pretreated cellulose showed remarkable enzymatic hydrolysability, despite an increase in its crystallinity to 72.3%. Contrary to conventional pretreatments, we report for the first time that the enzymatic hydrolysis of pretreated cellulose is enhanced by the removal of lignin during DE-THF pretreatment, notwithstanding an increase in its crystallinity. The current study paves way for the development of newer strategies for biomass depolymerization with DES based solvents.

scholarly journals Hydrogenation of secondary amides using phosphane oxide and frustrated Lewis pair catalysis

2021 ◽  
Author(s):  
Laura Köring ◽  
Nikolai A. Sitte ◽  
Markus Bursch ◽  
Stefan Grimme ◽  
Jan Henry Hakan Paradies
Keyword(s):  
Frustrated Lewis Pair ◽  
Secondary Amides

Bis(perchlorocatecholato)silane and Heteroleptic Bidonors: Hidden Frustrated Lewis Pairs by Ring Strain

2021 ◽  
Author(s):  
Deborah Hartmann ◽  
Sven Braner ◽  
Lutz Greb
Keyword(s):  
Ammonia Borane ◽  
Frustrated Lewis Pairs ◽  
Ring Strain ◽  
Frustrated Lewis Pair ◽  
Lewis Pairs

Bis(perchlorocatecholato)silane and bidentate N,N- or N,P-heteroleptic donors form hexacoordinated complexes. Depending on the ring strain and hemilability in the adducts, Frustrated Lewis pair reactivity with aldehydes and catalytic ammonia borane...

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