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Organocatalysis in a confined space has been performed through encapsulation of a proazaphosphatrane superbase in a hemicryptophane host. The resulting catalyst displays good to high catalytic activity in the base-catalyzed Diels-Alder reactions investigated. A comparison with the model superbase, which lacks a cavity, shows much higher diastereomeric excess with the encaged proazaphosphatrane for the reaction of 3-hydroxy-2-pyrone with N-methylmaleimide. The use of an encaged superbase as organocatalyst is unprecedented and highlights how the confinement may impact the stereoselectivity. [ABSTRACT FROM AUTHOR]

Catalytic materials bearing multiple sulfonic acid functional groups and positioned at varying distances from one another on the surface of mesoporous solids are prepared to explore the effects that the spatial arrangement of active sites have on catalytic activity and selectivity. A series of organosiloxane precursors containing either disulfide or sulfonate ester functionalities (synthons of the eventual sulfonic acid groups) are synthesized. From these molecular precursors, a variety of organic-inorganic hybrid, mesostructured SBA-15 silica materials are prepared using a postsynthetic grafting procedure that leads to disulfide and sulfonate ester modified silicas: [Si]CH[sub 2]CH[sub 2]CH[sub 2]SS-pyridyl, 2·SBA, [Si]CH[sub 2]CH[sub 2]CH[sub 2]SSCH[sub 2]CH[sub 2]CH[sub 2][Si], 3·SBA, [Si]CH[sub 2]CH[sub 2](C[sub 6]H[sub 4])(SO[sub 2])OCH[sub 2]CH[sub 3], 4·SBA, and [Si]CH[sub 2]CH[sub 2](C[sub 6]H[sub 4])(SO[sub 2])OC[sub 6]H[sub 4]O(SO[sub 2])(C[sub 6]H[sub 4])CH[sub 2]CH[sub 2][Si], 6·SBA ([Si] = (≡-SiO)[sub x](RO)[sub 3-x]Si, where x = 1,2). By subsequent chemical derivatization of the grafted species, thiol and sulfonic acid modified silicas are obtained. The materials are characterized by a variety of spectroscopic ([sup 13]C and [sup 29]Si CP MAS NMR, X-ray diffraction) and quantitative (TGA/DTA, elemental analysis, acid capacity titration) techniques. In all cases, the organic fragment of the precursor molecule is grafted onto the solid without measurable decomposition, and the precursors are, in general, attached to the surface of the mesoporous oxide by multiple siloxane bridges. The disulfide species 2·SBA and 3·SBA are reduced to the corresponding thiols 7·SBA and 8·SBA, respectively, and 4·SBA and 6· SBA are transformed to the aryl sulfonic acids 11·SBA and 12·SBA, respectively. 7·SBA and 8·SBA differ only in terms of the level of control of... [ABSTRACT FROM AUTHOR]

The synthesis and characterization of heterogeneous catalysts containing surfaces functionalized with discrete pairs of sulfonic acid and thiol groups are reported. A catalyst having acid and thiol groups separated by three carbon atoms is ca. 3 times more active than a material containing randomly distributed acid and thiol groups in the condensation of acetone and phenol to bisphenol A and 14 times more active in the condensation of cyclohexanone and phenol to bisphenol Z. Increasing the acid/thiol distance in the paired materials decreases both the activity and selectivity. This work clearly reveals the importance of nanoscale organization of two disparate functional groups on the surface of heterogeneous catalysts. [ABSTRACT FROM AUTHOR]

We report on the synthesis of C 3 -symmetric enantiopure cage molecules 1 , which exhibit remarkable to exclusive enantioselective recognition properties toward chiral ammonium neurotransmitters. Strong changes in the substrate selectivity are also observed when different stereoisomers of 1 are used. Furthermore, protonation/deprotonation induces a reversible modification of the conformation of 1 , which switches from an imploded to an inflated form, leading to ejection and reuptake of the guest initially encaged inside the cavity.

Hemicryptophanes are host molecules with many applications as supramolecular catalysts or in ion selective recognition. A very convenient and efficient modular approach for the synthesis of hemicryptophane-tren (tren, tris(2-aminoethyl)-amine) derivatives has been developed. For instance, hemicryptophane 1 was synthesized at the gram scale in four steps from vanillyl alcohol compared to the previous seven-step procedure. The size, shape, and functionalities of the molecular cavity were also easily modified., (© 2011 American Chemical Society)