Attempted [2]Catenane Synthesis via a Quasi[1]catenane by a Templated Backfolding Strategy

Abstract

A templated backfolding concept to construct a [2]catenane was attempted via a quasi [1]catenane showing an inverted spiro geometry. The template is covalently connected to the ketal-connected semi-perpendicular-arranged linear pre-

Template‐Directed Synthesis of an Inverted Spiro Architecture

“…In our endeavors to develop a novel methodology towards entangled molecules, for which the current supramolecular approaches fall short, we recently disclosed a covalent approach towards inverted spiro multicycles, also named as quasi[1]catenanes . However, these inverted macrocyclic spiro compounds still contained a central tetrahedral carbon atom that is part also of a five‐membered fluorene‐centered cyclopentadiene or ketal, similar to Schill's precatenane 4 . In this communication we describe the successful targeted synthesis of the truly bicyclic inverted spiro [27,27]‐membered bicycle 3 , that is, where the central carbon atom is the sole linkage between macrocycles (Scheme ).…”

An Inhospitable Cryptand: The Importance of Conformational Freedom in Host‐Guest Complexation

“…four atoms. Some systems called quasi [1]catenanes have also been reported; these consist of two rings sharing a spiro linkage constructed by step‐wise chemistry a la Schill . It seems that no pseudo [1]catenane of the sort shown in Figure formed by hydrogen bond induced self‐threading across the width of the initial macrocycle has been reported.…”

[2]Catenane Synthesis via Covalent Templating

“…Refluxing in CH 2 Cl 2 for 3 days gave cage compound 23 b in 24 % yield. Compared to 23 a , [30] 23 b is formed in lower yield and showed a much simpler 1 H‐NMR spectrum, with only minor splitting of the signals corresponding to chemically equivalent protons. These surprising differences suggest the presence of substantial interactions between the macrocycle amides and the tartrate core in 23 a , resulting in rigidification of the macrocycle (in red) and slowing down conformational exchange.…”

“…By following the backfolding templated strategy as outlined in Scheme 1 B and using the powerful Cu I ‐catalyzed azide‐alkyne cycloaddition (CuAAC) and ring‐closing metathesis (RCM) as the key macrocyclization steps, precatenane 9 a was successfully obtained. However, to our surprise but even more disappointment, all attempts at hydrolyzing the acid labile ketal group failed [30] . Initially this was attributed to steric shielding within the very congested precatenane architecture.…”

“… Comparison of 1 H‐NMR spectra of trivial spiro bicycle 27 a (I) and precatenane 9 a [30] (II) in CDCl 3 . For proton assignments, see Scheme 6.…”