Cooperative capture synthesis: yet another playground for copper-free click chemistry

Abstract

Click chemistry describes a family of modular, efficient, versatile and reliable reactions which have acquired a pivotal role as one of the most useful synthetic tools with a potentially broad range of applications. While copper(i)-catalysed alkyne-azide cycloaddition is the most widely adopted click reaction in the family, the fact that it is cytotoxic restricts its practice in certain situations, e.g., bioconjugation. Consequently, researchers have been exploring the development of copper-free click reactions, the most popular example so far being strain-promoted alkyne-azide cycloadditions. An early example of copper-free click reactions that is rarely mentioned in the literature is the cucurbit[6]uril (CB6) catalysed alkyne-azide cycloaddition (CB-AAC). Despite the unique ability of CB-AAC to generate mechanically interlocked molecules (MIMs) - in particular, rotaxanes - its slow reaction rate and narrow substrate acceptance limit its scope. In this Tutorial Review, we describe our efforts of late in developing the fundamental principles and practical applications of a new copper-free click reaction - namely, cooperative capture synthesis, whereby introducing a cyclodextrin (CD) as an accelerator in CB-AAC, hydrogen bonding networks are formed between the rims of CD and CB6 in a manner that is positively cooperative, giving rise to a high level of pre-organisation during efficient and quick rotaxane formation. For example, [4]rotaxanes can be prepared nearly quantitatively within a minute in water. Furthermore, we have demonstrated that CB-AAC can accommodate a wider substrate tolerance by introducing pillararenes as promoters. To date, we have put cooperative capture synthesis into practice by (i) preparing polyrotaxanes containing up to 200 rings in nearly quantitative yields, (ii) trapping conformational isomers of polymacrocycles as rings in rotaxanes, (iii) demonstrating solid-state fluorescence and Förster resonance energy transfer (FRET) processes by fixing the fluorophores in a rotaxane and (iv) establishing the principle of supramolecular encryption in the preparation of dynamically and reversibly tunable fluorescent security inks.

Strain‐Promoted Reactivity of Alkyne‐Containing Cycloparaphenylenes

“…20)isthe rate-determining step followed by rapid first-order RC ring opening (20 ! More than [2+ +2]CA-RC reactions,S PA AC reactions are highly important within the realm of click chemistry in awide range of chemical disciplines,including materials science [21][22][23] and chemical biology. Fort he ratedetermining step (DG°2 98 K = 22.1 AE 0.6 kcal mol À1 )t he entropic contribution (DS°= À37.5 AE 1.0 cal K À1 mol, at 298 K: DS°2 98 K = À11.2 AE 0.3 kcal mol À1 )s lightly exceeds that of the enthalpy (DH°= 10.9 AE 0.3 kcal mol À1 ;Supporting Information, Figure S44, Table S1).…”

“…The development of archetypal angle-strained alkynes that have laid the foundationsf or aryne and bioorthogonalchemistry; starting from 1,2-didehydrobenzene [8] and cyclooctyne in the 1950s. Moreover,w ea lso demonstrate that these structures can undergo facile and high-yielding SPAAC reactions,t herefore opening the door to ar ange of applications in materials science [21][22][23] and chemical biology. Moreover,w ea lso demonstrate that these structures can undergo facile and high-yielding SPAAC reactions,t herefore opening the door to ar ange of applications in materials science [21][22][23] and chemical biology.…”

Recognition of Different Metal Cations by a trans‐4‐[4‐(Dimethylamino)styryl]‐1‐methylpyridinium Iodide@Tetramethylcucurbit[6]uril Probe

“…Cucurbit[n]urils (Q[n]s) [1][2][3][4][5][6] are generally characterized by a nearly neutral electro-potential cavity and two negative electro-potential carbonyl-fringed portals, in addition to a positive electro-potential outer surface: the cavities of Q[n]s can accommodate various guest molecules through hydrophobic interactions, resulting in characteristic cucurbit[n]uril chemistry known as Q[n]-based host-guest chemistry; [7][8][9][10][11][12][13][14][15][16][17] Additionally, carbonyl groups on the rims of the portals of Q[n]s can interact with metal ions through direct coordination, resulting in distinct Q[n]-based coordination chemistry; [18][19][20][21] Furthermore, the positive electro-potential outer surface of Q[n]s can induce the formation of various novel supramolecular assemblies thorough the outer surface interaction of cucurbit[n]urils, which is another emerging research field in cucurbit[n]uril chemistry. [22] To date, Q[n]-based host-guest chemistry and Q[n]based coordination chemistry have received most attention in Q[n] research, including molecular machines or switches, [23] materials science, supramolecular materials and polymers, [15,24] life science, [25] catalysis, [13,14] sensors and other applications.…”

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Based on the study of a known host-guest inclusion complex comprising cucurbit [6]uril (Q[6]) and a hemicyanine dye, trans-4- [4-(dimethylamino)styryl]-1-pyridinium iodide (t-DSMI), a water-soluble symmetric tetramethylcucurbit[6]uril (TMeQ[6]), was selected to construct a t-DSMI-based probe to test the response to various metal cations in neutral water. [22] To date, Q[n]-based host-guest chemistry and Q[n]based coordination chemistry have received most attention in Q[n] research, including molecular machines or switches, [23] materials science, supramolecular materials and polymers, [15,24] life science, [25] catalysis, [13,14] sensors and other applications.Cucurbit[n]urils (Q[n]s) can interact with both guests (G) and metal cations (M n+ ), respectively. ">Introduction

Cucurbit[n]urils (Q[n]s) [1][2][3][4][5][6] are generally characterized by a nearly neutral electro-potential cavity and two negative electro-potential carbonyl-fringed portals, in addition to a positive electro-potential outer surface: the cavities of Q[n]s can accommodate various guest molecules through hydrophobic interactions, resulting in characteristic cucurbit[n]uril chemistry known as Q[n]-based host-guest chemistry; [7][8][9][10][11][12][13][14][15][16][17] Additionally, carbonyl groups on the rims of the portals of Q[n]s can interact with metal ions through direct coordination, resulting in distinct Q[n]-based coordination chemistry; [18][19][20][21] Furthermore, the positive electro-potential outer surface of Q[n]s can induce the formation of various novel supramolecular assemblies thorough the outer surface interaction of cucurbit[n]urils, which is another emerging research field in cucurbit[n]uril chemistry.

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Alkali Metal Ion-enhanced Threading of a Perylenediimide-bound Polymer Chain through a Double-stranded Spiroborate Helicate with a Bisporphyrin Unit

“…4 Nolte, Rowan, and co-workers took advantage of this unique biological rotaxane formation and succeeded in the construction of an artificial rotaxane system composed of a catalyticallyactive porphyrin-based macrocycle that threaded onto a reactive polymer chain during oxidation along the polymer, 5 and further proposed a unique threading mechanism of porphyrin-based macrocycles onto a viologen-appended polymer chain bearing a bulky stopper at one end as a model system, 6 through which the macrocycles thread from the polymer chain in one direction to form a 1:1 inclusion complex with the terminal viologen residue of the polymer. Although a large number of supramolecular rotaxane and pseudorotaxane formations have been reported, 1,2,7 biomimetic pseudorotaxane complex formation between macrocycles and polymers focusing on such a polymer threading process before complexation remains limited. …”