Thermally and Photochemically Induced Dethreading of Fumaramide‐Based Kinetically Stable Pseudo[2]rotaxanes

Abstract

The thermally and photochemically induced dethreading of a series of pseudo[2]rotaxanes bearing tetraalkyl‐substituted fumaramide axles and polyamide macrocycles is reported herein. The length of the alkyl chains at the ends of the thread, the void size, and flexibility of the macrocycle and the intercomponent interactions are critical for a satisfactory dethreading process. 1H NMR kinetic experiments were carried out in order to calculate the rate constants of the thermal dethreading processes and stabilities of the rotaxanes, by comparing with the similar data for the deslipping of the succinamide surrogates. The deslipping reaction occurs faster with the fumaramide systems than succinamide ones. The incorporation of adamantane moieties into the polyamide macrocycle drastically slowed down the disconnecting process. Furthermore, interlocked systems with dipropylamino groups as stoppers experienced a rapid dethreading when irradiated under UV‐light, a process triggered by the fumaramide–maleamide isomerization. In this case, the n‐propyl groups are not bulky enough to keep together both components as the number of hydrogen bonds between thread and macrocycle is halved in the maleamide systems.

Synthesis of an Adamantane-Based Tetralactam and Its Association with Dicarboxamides

“…The advantage of the initial synthesis of the rotaxane 2 resides in its easy isolation from other reaction byproducts. The obtained yield was lower than the those reported for other tetraalkyl fumaramide analogs with an isophthaloyl-based macrocycle [15], a consequence of the lesser acidity of the hydrogens of the amides for the macrocycle and, thus, a lower stability of the different supramolecular intermediates. The next step consisted of a thermal dethreading of rotaxane 2 to afford the free macrocycle 1 (Scheme 2) [12].…”

“…The resulting solid was subjected to column chromatography (silica gel) to yield unconsumed thread and [2]rotaxane 2 (141 mg, 5%). Rotaxane 2 showed identical spectroscopic data to those reported in [15].…”

“…The solid residue was filtered and washed with pentane, giving the title product as a white solid (58 mg, 80 %). Macrocycle 1 showed identical spectroscopic data to those reported in [15].…”

“…In one of our research programs focused on the development of novel hydrogen-bonded rotaxanes [9][10][11][12][13][14][15][16], we described the preparation of kinetically stable pseudorotaxanes [12,15] bearing benzylic amide macrocycles and a dicarboxamide-based template such as fumaramides or succinamides. These studies settled the structural requirements of the interlocked systems to allow the dethreading reaction and their kinetic parameters under thermal and photochemical treatments.…”

Five-component, one-pot synthesis of an electroactive rotaxane comprising a bisferrocene macrocycle

“…Threads containing an ester group were selected as esters could potentially be hydrolysed post-clipping to allow isolation of the macrocycle. The diamide/ bisamide thread had flexible stoppers, which may enable dethreading by slippage in a polar solvent as previously observed [5,16].…”