Assembling triazolated calix[4]semitubes by means of copper(i)-catalyzed azide–alkyne cycloaddition

Abstract

Nine pairs of cone and 1,3-alternate calix[4]arenes having distal propargyl or 2-azidoethyl groups at their phenolic oxygens were thoroughly studied at macrocyclization under copper(I) catalysis (CuAAC, copper(I)-catalyzed azide-alkyne cycloaddition). Though...

Triazolated calix[4]semitubes: assembling strategies towards long multicalixarene architectures

“…The calixarenes of the first type are the respective bis(azides) or bis(alkynes) which can be used as the terminal units at both sides of a semi-tube, while the calixarenes of the other type are those having two pairs of azide or/and alkyne groups separated from each other by the macrocyclic core. Calix[4]arenes 1 , 10 and 2–4 8 bearing 2-azidoethyl groups (Fig. 1) were selected as the bisazide terminal units in the triazolated calix[4]semitubes, and the structurally related calixarene dipropargyl ethers 5 , 11 6 , 12 7 , 13 and 8 8 were used as the bisalkyne terminal units.…”

“…Calix[4]arenes 1 , 10 and 2–4 8 bearing 2-azidoethyl groups (Fig. 1) were selected as the bisazide terminal units in the triazolated calix[4]semitubes, and the structurally related calixarene dipropargyl ethers 5 , 11 6 , 12 7 , 13 and 8 8 were used as the bisalkyne terminal units. Within each of the series, the bifunctional molecules have free phenolic OH groups or those propylated to fix the calix[4]arene macrocycle in a cone or 1,3-alternate molecular shape.…”

“…Within each of the series, the bifunctional molecules have free phenolic OH groups or those propylated to fix the calix[4]arene macrocycle in a cone or 1,3-alternate molecular shape. Notably, the bis(azides) or bis(alkynes) of each type have been shown to react with each other to form the respective biscalixarene semitubes, 8 so they were expected to be suitable for building longer semitubes as well.…”

“…8 Reasonably, successful preparation of the triscalixarene semitubes using tetrafunctional central cores 9 or 11 requires the same or even more strict tuning of the reaction conditions. Still, the conditions obtained previously for the preparation of a semitube from 1,3-alternate bis(alkyne) 8 and cone bis(azide) 1 8 were found suitable also for the reaction between the bis(azide) 1 and the tetrakis(alkyne) 9 taken in a 2 : 1 molar ratio (Scheme 2). Indeed, the reaction conducted in the presence of 0.3 equiv.…”

“…We have recently shown 8 that diverse biscalixarene semi-tubes may be constructed from the respective bisazide and bisalkyne calixarene precursors using copper( i )-catalyzed azide–alkyne cycloaddition (CuAAC). 9 Each of these assemblies comprises a single binding site formed by two 1,4-disubstituted 1,2,3-triazole groups surrounded by the calixarene cores and targeted to transition cations.…”