Concave reagents syntheses

Luning. U. Concave reagents Syntheses of macrobicyclic pyridines. Liebigs Ann. Chem. 1987. 949-955. 

In the case of catalytic systems, the tedious and expensive synthesis of a concave catalyst is compensated by its (theoretically) unlimited recyclability. Reagents, in contrast, are used up in a reaction. Therefore, concave reagents will only be attractive when, after the reaction, the used functional groups can be returned into the active original functionality. They must be rechargeable . This is trivial for acids and bases but in principle should also be realizable for redox reagents. 

S. LUthje, C. Bomholt, U. Liining, Concave reagents, 46 polyols as templates for the synthesis of macrocycles from boronic acid bnilding blocks, Eur. J. Org. Chem., 2006, 909-915. 

H. Ross, U. Liining, Concave reagents, 19 synthesis, structure and basicity of a calix[6]arene bridged by an aniline, Tetrahedron, 1996, 52, 10879-10882. 

O. Winkelmann, C. Nather, U. Liining, Concave reagents, 56 synthesis, structure and catalytic activity of a himacrocyhc NHC palladium allyl complex, J. Organomet. Chem., 2008, 693, 2784-2788. 

Carcerands and Hemicarcerands, p. 189 Concave Reagents, p. i /1 Crown Ethers, p. 326 Cryptophanes, p. 340 Cyclodextrins, p. 398 Cyclodextrins, Applications, p. 405 Cyclophanes Definition and Scope, p. 414 Enzyme Mimics, p. 546 Macrocycle Synthesis, p. 830 Organometallic Anion Receptors, p. 1006 Soft and Smart Materials, p. 1302 X-Ray Crystallography, p. 1586... 

To justify the synthetic efforts for the synthesis of concave reagents, the gain in selectivity must be combined with an easy recovery. Usually, polymer fixation allows easy recycling, and therefore, the concave pyridine la has been attached to a Merrifield resin (27, see Fig. 8a).Indeed, the polymeric material 27 was able to catalyze the alcohol addition to diphenylketene comparably to the soluble concave pyridine la. but complications may exist due to swelling of the resin and substrate depletion deep within the polymer. Therefore, soluble polymers loaded with the concave pyridine I a have also been synthesized. However, this material behaved unreproducibly, especially because side reactions led to cross-polymerized insoluble material. Furthermore, due to reptation (leakage through membrane), an easy separation of product and catalyst would not be possible by ultrafiltration. 

Liining. U. Baumstark. R. Peters. K. von Schnering, H.G. Concave reagents, 3 Synthesis, basicity and conformation of new concave pyridines. Liebigs Ann. Chem. 1990. 129-143. 

Ross. H. Luning. U. Concave reagents. 23 Synthesis of a calix[6]arene bridged by a 1.10-phenanthroline. Tetrahedron Lett. 1997. 38. 4539-4542. 

Ross. H. Liining, U. Concave reagents. 18 Synthesis, conformational behaviour, and basicit of new pyridine-bridged calix[6Jarenes Liebigs Ann 1996. 1367-1373... 

Liining. U. Baumgartner. H. Concave reagents. 13 2 -Substituted m-terphenyls as building blocks. Synthesis of a concave thiol acetate. Synlett 1993. 571-572. 

For weak acids, the proton is directly transferred from the acid to the substrate in a reagent-controlled manner and, in order to increase the selectivity, extremely shielded 2 -substituted m-terphenyls have been developed as concave protonating reagents inspired by the geometry of enzymes. Thus, the diastereoselective protonation by a series of substituted phenols of endocyclic keto enolates, obtained by the stereocontrolled 1,4-addition of lithiocuprates onto substituted cyclohexenones, was reported by Krause and coworkers354 355 and applied to the synthesis of racemic methyl dihydroepijasmonate356. 

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