Binary acid catalysis

In the absence of a catalytic amount of Lewis acids such as Mg(OTf)2, weak Bronsted acids, such as thioureas, BINOL, and BINOL-derived phosphoric acids, could not promote this reaction alone. The reaction could not proceed with phosphoric acid salts, suggesting that the use of free acid is essential for effective catalysis. The combination of chiral phosphoric acid 13e and Lewis acid Mgp2 (4 1 ratio) was identified to be the optimal catalyst for the AFC alkylation reactions of phenols with p,y-unsaturated a-keto esters, affording the alkylation product in good yields with up to 99% ee. Not only free phenols but also indoles could be successfully applied in AFC reactions with P,y-unsaturated a-keto esters under the binary-acid catalysis (82-94% ee). 

This unexpected finding encouraged them to further explore the factors that control the regioselectivity in this AFC reaction. Further experiments were carried out to disclose a clear picture of the binary acid catalysis. Besides the critical role of such binary acids in stereocontrol, the judicious selection of chiral phosphoric acid, Lewis acid and combination is essential... 

Scheme 6.33 Enantioselective 1,2- and 1,4-addition of N-protected indoles with a-keto esters catalyzed by binary-acid catalysis reported by Luo.

Asymmetric binary acid catalysis Chiral phosphoric acid as dual hgand and acid 13CC847. 

Scheme 8 Catalytic enantioselective t rt-amino cyclization by asymmetric binary acid catalysis...

Binary systems of ruthenium sulfide or selenide nanoparticles (RujcSy, RujcSey) are considered as the state-of-the-art ORR electrocatalysts in the class of non-Chevrel amorphous transition metal chalcogenides. Notably, in contrast to pyrite-type MS2 varieties (typically RUS2) utilized in industrial catalysis as effective cathodes for the molecular oxygen reduction in acid medium, these Ru-based cluster materials exhibit a fairly robust activity even in high methanol content environments of fuel cells. 

Other examples of ancillary ligands used to enhance analyte selectivity include amide-modified D03A (1,4,7,10-tetraazacyclododecane-l,4,7-trisacetate) complexed to Tb , which selectively binds the bidentate analytes p-dimethylaminobenzoic acid (DMABA) and SA (160-162). The binary complex of with EDTA can effectively detect SA, 4-aminosalicylic acid and 5-fluorosalicylic acid (163). [Tb(EDTA)] also has been used to detect catalysis of hydroxybenzoic acid (HBA) by hemin via formation of a ternary complex with the HBA oxidation product (164). Diaza-crown ethers have been utilized with and Eu to detect phthalate, benzoate,... 

Lecrenay, E., Sakanishi, K., Mochida, I., and Suzuka, T. Hydrodesulfurization activity of CoMo and NiMo catalysts supported on some acidic binary oxides. Applied Catalysis. A, General, 1998, 175, 237. 

Hu et al. developed a system that involved cooperative catalysis by a chiral phosphoric acid and an achiral rhodium complex (Scheme 3.37) [81]. They applied the binary catalytic system to a three component coupling reaction among a diazoesters, primary alcohols, and aldimines. The steric bulkiness of the primary alcohol had a significant effect on both diastereo and enantioselectivities. The sterically demanding 9 anthracenemethanol was the best component to give p amino a alkoxy esters with excellent stereoselectivities under the combined and cooperative catalysis by phosphoric acid ll and the rhodium complex. 

Scheme 3.38 Relay catalysis by ruthenium complex/Bronsted acid binary system.

The enantioselective version of the relay transformation by organic and metallic catalyses was successfully demonstrated by Gong and coworkers (Scheme 3.39) [83]. They accomplished the direct transformation of o propargylaniline derivatives into tetrahydroquinolines in a highly enantioselective manner through the hydroamina tion of alkynes/isomerization/enantioselective transfer hydrogenation (see Sec tion 3.3 for details) sequence under the relay catalysis of an achiral Au complex/ chhal phosphoric acid binary system. 

At. M. Oxidation activity and acid-base properties of tin dioxide-based binary catalysts. I. Tin dioxide-vanadium pentoxide system. Journal of Catalysis 1975 40, 318-326. 

A novel protocol described the direct conversion of 2-(2-propynyl)aniline derivatives (128) into tetrahydroquinolines (129) in high enantioselectivities, in one operation, through a consecutive hydroamination of alkynes/asym-metric transfer hydrogenation reactions under the catalysis of an achiral Au complex and the chiral phosphoric acid (124) binary system (Scheme 31). ... 

For the system methyl acetate-acetic acid-methanol-water he determined VLE data for all six binary systems, unless thermodynamically consistent values were already available from literature, for the four ternary systems and for the quaternary system with and without the catalyst. It was found that the presence of sulphuric acid in the composition range of up to 4 wt-%, as normally encountered in homogeneous catalysis, had negligible effect on the equilibrium data calculated on acid-free basis. 

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