Supramolecular Catalysts Featuring Crown Ethers as Recognition Units

Abstract

In its minimal expression, a supramolecular catalyst that acts on a single bound substrate consists of (i) a binding unit that is complementary to a non‐reacting part of the substrate, (ii) a reactive unit capable of catalyzing the reaction of the bound substrate, and (iii) a spacer connecting the two units in a geometry suitable for productive binding. When binding of two or more species is wanted, the number of binding units increases accordingly. This minireview deals with supramolecular catalysts that use crown ether units for the recognition of one or two reactants involved in a variety of reactions, including cleavage of esters and amides, hydride transfer from dihydropyridine to pyridinium, pyruvate decarboxylation, enolate allylation, radical addition to sodium metacrylate, reduction of NO2– anion to NO, C–H oxidation of aliphatic chains, and Diels‐Alder reactions.

Predictable Selectivity in Remote C−H Oxidation of Steroids: Analysis of Substrate Binding Mode

“…1 H NMR monitoring of the binding of the amino‐steroid 1 to ( R , R )‐( CR pdp)Zn suggests a 2:1 stoichiometry (see Figures S2–S5), akin to that previously observed for linear ammonium ions, with each crown ether hosting one guest to form a symmetric adduct (Figure A; see Figures S2 and S3). Further evidence for such 2:1 stoichiometry comes from the loss and subsequent recovery of the fine structure of the benzocrown NMR signals during the titration, consistent with initial 1:1 adducts with lower symmetry (loss of signal definition) that eventually form symmetric 2:1 structures after the equivalence (see Figure S4) .…”

Feet‐to‐Feet‐Connected Multitopic Resorcinarene Macrocycles

“…Thus, the macrocyclization of resorcinol and bisdioxolanes 6 f-h appeared to smoothly proceed in fairly good yields. In their 1 H and 13 C NMR spectra, the aromatic protons and aromatic carbons were split into a pair, which indicates that the resorcinol units are pairwise in two distinct magnetic fields. The D 3h symmetric features of 14 a-c were spectroscopically established.…”

“…[1][2][3][4][5][6] Inspired by sophisticated macrocycles, considerable effort has been devoted to the development of engineered macrocycles. [7] Resorcinarenes [8][9][10][11] are exciting synthetic macrocycles that, like crown ethers, [12][13][14] cyclodextrins, [15] calixarenes, [16][17] calixpyrroles, [18][19] and pillararenes, [20] possess diverse applications in host-guest chemistry ( Figure 1). A resorcinarene is typically prepared by condensation of resorcinol and appropriate aldehydes, as described by Cram et al [21] The cone-shaped cavity of resorcinarene is maintained by four interannular hydrogen bonds between the resorcinol units, which affords high binding affinity with small hydrogen-bonding guest molecules.…”

“…Inspired by sophisticated macrocycles, considerable effort has been devoted to the development of engineered macrocycles [7] . Resorcinarenes [8–11] are exciting synthetic macrocycles that, like crown ethers, [12–14] cyclodextrins, [15] calixarenes, [16–17] calixpyrroles, [18–19] and pillararenes, [20] possess diverse applications in host–guest chemistry (Figure 1). A resorcinarene is typically prepared by condensation of resorcinol and appropriate aldehydes, as described by Cram et al [21] .…”

Selecting Double Bond Positions with a Single Cation- Responsive Iridium Olefin Isomerization Catalyst

“…[21][22][23][24][25] Noncovalent modification has been particularly impactful in the field of alkene hydroformylation, with additives (including alkali metal cations.) [26][27][28][29][30][31] interacting with the catalyst to tune the aldehyde regioselectivity between terminal or secondary positions. 32 Finding a single catalyst that can access two states that are different enough to have dramatic differences in regioselectivity remains a challenge in hydroformylation.…”