Clickable Di- and Tetrafunctionalized Pillar[n]arenes (n = 5, 6) by Oxidation–Reduction of Pillar[n]arene Units

Abstract

We report a new route for the selective synthesis of di- and tetrafunctionalized pillararenes via oxidation and reduction of the pillararene units. Hypervalent-iodine oxidation of perethylated pillar[5]arene afforded pillar[5]arene derivatives containing one benzoquinone unit and two benzoquinones at the A,B- and A,C-units. A pillar[6]arene derivative containing one benzoquinone unit was also synthesized. Reduction of the benzoquinone units yielded position-selective di- and tetrahydroxylated pillararene derivatives. This methodology avoids the generation of many constitutional isomers and overcomes the isolation problem of numerous constitutional isomers. From these hydroxylated pillararenes, Huisgen reaction-based clickable di- and tetraalkynylated pillar[5]arenes were prepared. Because of the highly selective and reactive nature of Huisgen alkyne-azide cycloaddition, these pillar[5]arenes can serve as key compounds for a large library of di- and tetrafunctionalized pillararenes. Based on these di- and tetrafunctionalized pillar[5]arenes as key compounds, fluorescent sensors were created by the modification of di- and tetrapyrene moieties via Huisgen-type click reactions.

Synthesis of Pillar[n]arene[5−n]quinines via Partial Oxidation of Pillar[5]arene

“…[16][17][18] These reported oxidations were performed in tetrahydrofuran (THF) in the presence of water, taking long reaction time to complete (24 h or 48 h). In order to improve yields and shorten reaction time, we re-investigated the partial oxidation of 1 by CAN (Scheme 1).…”

“…Nonetheless, it was found that water is still needed like the reported oxidations. [16][17][18] The oxidation of 1 in pure CH 2 Cl 2 or CHCl 3 was hardly to go to complete even in extended reaction time (3 d) and the yields were very low. The structures of the oxidation products 2-5 were confirmed by the consistence of their NMR data and mass spectra (Supporting Information) with reported ones.…”

“…The structures of the oxidation products 2-5 were confirmed by the consistence of their NMR data and mass spectra (Supporting Information) with reported ones. [16][17][18] It is not quite clear why the yields and efficiency were improved when CH 2 Cl 2 or CHCl 3 was used to replace THF as reaction solvent, but a plausible explanation could be that the oxidation occurred more efficiently at the interface between aqueous and CH 2 Cl 2 (or CHCl 3 ) phases. (Figure 1), only single isomer was obtained predominantly, and isolated in the form of 3 or 4 in the present partial oxidation reactions.…”

Pillar-Shaped Macrocyclic Hosts Pillar[n]arenes: New Key Players for Supramolecular Chemistry

“…68,69 Oxidation of a 1,4-dialkoxybenzene unit in per-alkylated pillar [5]arenes afforded pillar [5]arenes with a benzoquinone unit (19 [5] and 20 [5]). Benzoquinone was easily converted to hydroquinone using a reducing agent; thus, the A1/A2 dihydroxylated pillar [5]arenes (25[5] and 26 [5]) were obtained by reduction of the benzoquinone unit.…”

“…Furthermore, pillar [5]arenes with two benzoquinone units at the A/B (21 [5] and 22 [5]) and A/C (23 [5] and 24 [5]) units can be prepared under the optimized oxidation condition, and reduction of these pillar [5]arenes with two benzoquinone units led to A1/A2/B1/B2 (27 [5] and 28 [5]) and A1/A2/C1/C2 (29 [5] and 30 [5]) tetra-hydroxylated pillar [5]arenes. 68 Tuning the oxidation condition enables the synthesis of pillar [5]arenes with three and four quinone moieties. Xue et al reported the synthesis of pillar [5]arenes consisting of three different kinds of units by selective oxidation of the units (Scheme 12).…”