Abstract
Macrocycles are unique molecular structures extensively used in the design of catalysts, therapeutics and supramolecular assemblies. Among all reactions reported to date, systems that can produce macrocycles in high yield under high reaction concentrations are rare. Here we report the use of dynamic hindered urea bond (HUB) for the construction of urea macrocycles with very high efficiency. Mixing of equal molar diisocyanate and hindered diamine leads to formation of macrocycles with discrete structures in nearly quantitative yields under high concentration of reactants. The bulky N-tert-butyl plays key roles to facilitate the formation of macrocycles, providing not only the kinetic control due to the formation of the cyclization-promoting cis C = O/tert-butyl conformation, but also possibly the thermodynamic stabilization of macrocycles with weak association interactions. The bulky N-tert-butyl can be readily removed by acid to eliminate the dynamicity of HUB and stabilize the macrocycle structures.
Highlights
Macrocycles are unique molecular structures extensively used in the design of catalysts, therapeutics and supramolecular assemblies
Macrocycles are synthesized through kinetic control in very dilute concentrations, which suffers from low yields and tedious purification processes[16]
We previously reported hindered urea bond (HUB) as a new dynamic covalent chemistry (DCC) tool[33], which can be synthesized from isocyanates and hindered amines, and can dissociate back to the starting compounds (Fig. 1e)
Summary
Macrocycles are unique molecular structures extensively used in the design of catalysts, therapeutics and supramolecular assemblies. Owing to their relatively rigid and defined scaffold, macrocycles are promising in biological sensing[1,2,3], ion transporting[4], drug discovery[5,6,7] and molecular sieving[8] Building on their propensity for self-assembly, macrocycles can serve as precursors to mechanically interlocked structures[9,10] and molecular machinery[11], and play an important role in catalysis[12] by providing nano-confinement[13]. The selective binding and associated host–guest interaction further dictate their usage in environmental pollutant removal[14] or drug delivery[15] Despite all these widespread applications, synthesis of macrocycles remains challenging, in particular under high concentration in large scale. DCCs are desired for the construction of macrocycles, in particular those of intrinsic hydrogen bonding capabilities which are of huge implications in molecular recognitions, self-assembly, molecular machinery and catalysis
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