The Hexameric Resorcinarene Capsule as a Brønsted Acid Catalyst for the Synthesis of Bis(heteroaryl)methanes in a Nanoconfined Space

Abstract

Herein, we show that the hexameric resorcinarene capsule C is able to catalyze the formation of bis(heteroaryl)methanes by reaction between pyrroles or indoles and carbonyl compounds (α-ketoesters or aldehydes) in excellent yields and selectivity. Our results suggest that the capsule can play a double catalytic role as a H-bond catalyst, for the initial activation of the carbonyl substrate, and as a Brønsted acid catalyst, for the dehydration of the intermediate alcohol.

Just Add Water: Modulating the Structure-Derived Acidity of Catalytic Hexameric Resorcinarene Capsules

“…The hydrogen-bond network of C11 R 6 results in the enhanced Brønsted acidity beyond that of the individual monomer units . This feature has driven the application of C11 R 6 as a supramolecular, organic Brønsted acid catalyst for chemical transformations under mild conditions. − In addition, the hydrogen-bond rich environment of the internal cavity within C11 R 6 has been utilized as a supramolecular organocatalyst, − demonstrating a host-selective reactivity based on substrate size, and substrate–bond activation via supramolecular interactions. The use of a supplemental protic acid cocatalyst (typically HCl) extends the scope of C11 R 6 activity, − notably for application toward facile synthesis of high-value terpene derivatives. − Further reactivity has been demonstrated in host-catalyzed Diels–Alder cyclization …”

Synthesis of a coumarin derivative of resorcin[4]arene with solvent-controlled chirality

“…12 Among other things, spatially developed structures such as cavitands, [13][14][15][16] dimeric capsules, [17][18][19][20] and hexamers [21][22][23][24] can be constructed based on such skeletons, and these can be used to study the reactivity of chemical compounds in spatially limited or closed structures. [25][26][27][28] One possibility for modifying the structure of resorcin [4] arene was our use of the methoxy derivative of resorcin [4]arene for the thermal generation of the o-quinone methide derivative of resorcin [4]arene, followed by a cycloaddition reaction [29][30][31] and Michael reaction with C, Pnucleophiles. 32,33 Until now, the synthesis of cyclochiral derivatives of resorcin [4]arene was based on two approaches: (1) structural modications of the skeleton of the resorcin [4]arene molecule via covalent bonds; 4,5 (2) on the selection of appropriate substrates for the synthesis of cyclochiral resorcin [4]arene molecules.…”

Kinetic and Thermodynamic Modulation of Dynamic Imine Libraries Driven by the Hexameric Resorcinarene Capsule

“…The capsule is obtained by self-assembly of six resorcinarene 1 and eight water molecules, sealed by 60 H-bonding interactions. The container CR 6 shows some features that make it a useful tool in biomimetic catalysis: (a) the internal π···electron-rich cavity of 1375 Å 3 is able to recognize neutral and cationic species and to stabilize transition states, due to secondary interactions; (b) the capsule CR 6 behaves as a mild Brønsted acid with a p K a value of about 5.5–6.0; (c) four bridging water molecules show a H-bond-donating free valence, which is catalytically relevant. , In addition, previously reported data show that the CR 6 capsule is able to exert a substrate selectivity, whereas stereo- and regioselectivity toward the products are also generally observed.…”