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-

Boronic ester-templated pre-rotaxanes as versatile intermediates for rotaxane endo -functionalisation

“…The use of dynamic covalent bonds for this purpose is critical, as bond cleavage in this system is facile and efficient, circumventing the stabilizing "catenand effect" that has hindered template removal in previous examples of covalently templates MIMs. 2,9 While the compounds in this work are largely articial, it should also be pointed out that the core binding motif here is the natural product L-tartrate. Polyhydroxylated scaffolds and vicinal diols are ubiquitous in nature (RNA, carbohydrates, natural products etc.…”

Boronic ester-templated pre-rotaxanes as versatile intermediates for rotaxane endo -functionalisation

“…The use of dynamic covalent bonds for this purpose is critical, as bond cleavage in this system is facile and efficient, circumventing the stabilizing "catenand effect" that has hindered template removal in previous examples of covalently templates MIMs. 2,9 While the compounds in this work are largely articial, it should also be pointed out that the core binding motif here is the natural product L-tartrate. Polyhydroxylated scaffolds and vicinal diols are ubiquitous in nature (RNA, carbohydrates, natural products etc.…”

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.…”

“…Furthermore, the NMR spectrum of catenane 10 b shows that the signals of both the terephthalate protons (c)a nd triazole protons (a)a ppear as double singlets ( Figure 3). This points to the presence of two diastereomeric forms of catenane 10 b,l ikely resulting Comparison of 1 H-NMR spectra of trivials pirob icycle 27 a (I) and precatenane 9a [30] (II) in CDCl 3 .For proton assignments, see Scheme6. from ac ombination of central chirality,e merging from the tartrate moiety,a nd planar chirality of the red macrocycle.…”

Boronic ester-templated pre-rotaxanes as versatile intermediates for rotaxane endo -functionalisation

“…The use of dynamic covalent bonds for this purpose is critical, as bond cleavage in this system is facile and efficient, circumventing the stabilizing "catenand effect" that has hindered template removal in previous examples of covalently templates MIMs. 2,9 While the compounds in this work are largely articial, it should also be pointed out that the core binding motif here is the natural product L-tartrate. Polyhydroxylated scaffolds and vicinal diols are ubiquitous in nature (RNA, carbohydrates, natural products etc.…”

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.…”

“…Furthermore, the NMR spectrum of catenane 10 b shows that the signals of both the terephthalate protons (c)a nd triazole protons (a)a ppear as double singlets ( Figure 3). This points to the presence of two diastereomeric forms of catenane 10 b,l ikely resulting Comparison of 1 H-NMR spectra of trivials pirob icycle 27 a (I) and precatenane 9a [30] (II) in CDCl 3 .For proton assignments, see Scheme6. from ac ombination of central chirality,e merging from the tartrate moiety,a nd planar chirality of the red macrocycle.…”

Boronic ester-templated pre-rotaxanes as versatile intermediates for rotaxane endo -functionalisation

“…The use of dynamic covalent bonds for this purpose is critical, as bond cleavage in this system is facile and efficient, circumventing the stabilizing "catenand effect" that has hindered template removal in previous examples of covalently templates MIMs. 2,9 While the compounds in this work are largely articial, it should also be pointed out that the core binding motif here is the natural product L-tartrate. Polyhydroxylated scaffolds and vicinal diols are ubiquitous in nature (RNA, carbohydrates, natural products etc.…”

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.…”

“…Furthermore, the NMR spectrum of catenane 10 b shows that the signals of both the terephthalate protons (c)a nd triazole protons (a)a ppear as double singlets ( Figure 3). This points to the presence of two diastereomeric forms of catenane 10 b,l ikely resulting Comparison of 1 H-NMR spectra of trivials pirob icycle 27 a (I) and precatenane 9a [30] (II) in CDCl 3 .For proton assignments, see Scheme6. from ac ombination of central chirality,e merging from the tartrate moiety,a nd planar chirality of the red macrocycle.…”