[2]Rotaxane Formation by Transition State Stabilization

Abstract

ABSTRACT:We report on the synthesis of [2]rotaxanes driven by stabilization of the axleforming transition state. A bifunctional macrocycle, with hydrogen bond donors at one end and acceptors at the other, is used to stabilize the charges that develop during the addition of a primary amine to a cyclic sulfate.Most rotaxanes are formed by exploiting permanent recognition motifs in the components that subsequently 'live on' in the interlocked product. 1 Examples of rotaxanes formed through complexdriven effective molarity increases or solvation effects have also been described, 2 and active template synthesis, 3 in which metal ions act as both an organizing template and as a catalyst for the reaction used to covalently capture the threaded structure, enables rotaxanes to be assembled under kinetic control. Here we describe the reagent-less formation of a [2]rotaxane driven by transition state stabilization of an activated complex arising from the opening of a cyclic sulfate by a primary amine. 4

Weak functional group interactions revealed through metal-free active template rotaxane synthesis

“…Active template synthesis [24][25][26][27][28][29][30][31][32][33][34][35] , in which a macrocycle accelerates a strand-forming reaction through the ring cavity, does not require strong pre-association of the starting materials. Although most active template syntheses have been developed from transition metal catalyzed reactions [24][25][26][27][28][29][30][31][32][33][34][35] , a metal-free active template system was recently discovered 36,37 in which the addition of primary amines to electrophiles can be significantly accelerated through crown ethers 37 and related macrocycles 36 by stabilization of the reaction transition state [38][39][40][41][42][43] . The reaction of a primary amine and an electrophile in the presence of a crown ether was found 37 to form [2]rotaxanes by metal-free active template Nalkylation, aza-Michael addition or N-acylation.…”

Template-Free Synthesis of a Phenanthroline-Containing [2]Rotaxane: A Reversible pH-Controllable Molecular Switch

“…Moreover, the signals for protons H 4 and H e were shifted downfield due to the removal of macrocycle 1 from the phenathroline site. In addition, the polyether protons (h, i, and j) are slightly upfield shifted and broadened, which results in hydrogen bonding interactions between the ether oxygen atoms and the ammonium hydrogen atoms [31,32]. The results thus indicate that macrocycle 1 moves to both of the oxyphenylene sites and the protonated aniline sites on either side upon the addition of acid.…”

Hypervalent Iodine Based Reversible Covalent Bond in Rotaxane Synthesis

“…However, the rotaxane formation with rods 2 and 3 unambiguously supports the proposed mechanism, as their substituents are too bulky to slip through the small BU cavity. It is worth noting that the system presented herein is one of the few examples of reagent‐less rotaxane preparations …”