[2]Catenane Synthesis via Covalent Templating

Abstract

After earlier unsuccessful attempts, this work reports the application of covalent templating for the synthesis of mechanically interlocked molecules (MiMs) bearing no supramolecular recognition sites. Two linear strands were covalently connected in a perpendicular fashion by a central ketal linkage. After subsequent attachment of the first strand to a template via temporary benzylic linkages, the second was linked to the template in a backfolding macrocyclization. The resulting pseudo[1]rotaxane structure was successfully converted to a [2]catenane via a second macrocyclization and cleavage of the ketal and temporary linkages.

Covalently Templated Syntheses of Mechanically Interlocked Molecules

“…A successful route was found from 32b by inclusion of ethylidene instead of the amide groups. 36 Ringclosing metathesis yielded 33b in moderate yield, after which catalytic hydrogenation and cleavage of temporary linkages resulted in precatenane 34b. Under strongly acidic conditions, the rings…”

“…37 Another distinguishing feature of the approach is the simultaneous capping and cleavage of the axle through aminolysis. Scheme 8 A successful and unsuccessful templated backfolding approach towards [2]catenane 35 using a cyclic ketal template 35,36 32a:…”

Template-Free Synthesis of an Interlocked Covalent Organic Molecular Cage

“…Mechanically interlocked molecules (MIMs) have attracted significant interest not only due to their aesthetically beautiful structures but also the unique properties originating from their interlaced nature. − It has been proven that MIMs like structures have inextricably woven into the life processes. − To obtain more insight into natural processes, artificial analogues are often created to help in better understanding the role of such topologies. Although remarkable progress has been achieved in recent years, the synthesis of MIMs such as catenanes, rotaxanes, Borromean rings, knots, and interlocked cages remains a synthetic challenge. − The rise of template synthesis , and reversible metal coordination bonds − have to a large extent overcome this limitation.…”

Covalent [2]Catenane and [2]Rotaxane Synthesis via a δ-Amino Acid Template

“…Inspired by the landmark directed synthesis of a catenane by Schill, 18 we recently prepared a [2]catenane by templated backfolding. 19 In both strategies, a ketal group was used to reversibly bind the separate fragments and enforce a perpendicular geometry between them before the key macrocyclizations. This preorganization is a strict requirement for the formation of the desired interlocked products.…”

“…To address the synthesis of so-called impossible MIMs, inaccessible by supramolecular templating, we embarked on the development of alternative covalent approaches. Inspired by the landmark directed synthesis of a catenane by Schill, we recently prepared a [2]­catenane by templated backfolding . In both strategies, a ketal group was used to reversibly bind the separate fragments and enforce a perpendicular geometry between them before the key macrocyclizations.…”