Template-controlled synthesis of chiral cyclohexylhemicucurbit[8]uril

Abstract

Enantiomerically pure cyclohexylhemicucurbit[8]uril (cycHC[8]), possessing a barrel-shaped cavity, has been prepared in high yield on a gram scale from either (R,R,N,N')-cyclohex-1,2-diylurea and formaldehyde or cycHC[6]. In either case, a dynamic covalent library is first generated from which the desired cycHC can be amplified using a suitable anion template.

Chiral hemicucurbit[8]uril as an anion receptor: selectivity to size, shape and charge distribution

“…42 V cavity ( cycHC[8] ) = 123.0 Å 3 is measured from the crystal structure of cycHC[8] . 31 b 1 H NMR in 1 : 1 MeOD/D 2 O.…”

“…To assess whether the low binding affinity of CF 3 SO 3 – is caused by the asymmetric charge distribution, a control experiment was conducted with CF 3 CO 2 – , similar in volume to PF 6 – , but with a charge distribution resembling that in CF 3 SO 3 – . The fact that CF 3 CO 2 – , which effectively templates the synthesis of cycHC[8] (in acetonitrile) and has been shown by diffusion NMR to bind to cycHC[8] in chloroform, 31 does not bind to cycHC[8] in methanol ( K a < 10), indicates that the binding of anions to cycHC[8] in methanol is sensitive to charge distribution around the anion.…”

“…31 Moreover, it proposes a pathway to and encourages the preparation of new hemicucurbiturils for anion binding and transport, catalysis in confined space and other supramolecular applications.…”

Templating Effects in the Dynamic Chemistry of Cucurbiturils and Hemicucurbiturils

“…In the case of hemicucurbit [12]uril this leads to the highly efficient formation of a covalently bound chain of 48 atoms. [15] A computational study on the pathway of acyliminium intermediate formation from ethyleneurea and formaldehyde was recently published by Yoo and Kang, [29] which shows the involvement of urea carbonyl group during iminium formation (Scheme 3, A).Importance of C=O group during formation of bambusurils has been experimentally observed by Reany and Keinan, [14] as the condensation of formaldehyde with thio-analogue of ethyleneurea (Scheme 3, B) does not result in formation of thioacylaminal linker. Influence of the chain-growth and chain-cycle equilibrium and the effect of different templates in CB chemistry is discussed.…”

Size‐Control by Anion Templating in Mechanochemical Synthesis of Hemicucurbiturils in the Solid State

“…Despite advances in understanding the kinetics and thermodynamics [4] of mechanochemistry,factors directing the formation of complex molecular structures [5] under such conditions remain unexplored. [7] Single-bridged cucurbiturils,h emicucurbiturils,i ncluding bambusurils and biotinurils,are macrocyclic hosts formed by anion-templated synthesis, [8] with use in anion [9] and chirality [10] recognition, anion transport, [11] catalysis, [12] and photoinduced electron transfer. [7] Single-bridged cucurbiturils,h emicucurbiturils,i ncluding bambusurils and biotinurils,are macrocyclic hosts formed by anion-templated synthesis, [8] with use in anion [9] and chirality [10] recognition, anion transport, [11] catalysis, [12] and photoinduced electron transfer.…”