Molecular Ribbons Containing Pyridine Rings

Abstract

The first synthesis of the ribbon-like compounds 6-10 is a face-to-face manner, and the tosyl units of 8-10 pointing described. The new building block diethyl 2,6-bis(bromo-outwards. The "intramolecular self-assembly" (folding) of methyl)pyridine-3,5-dicarboxylate 1 was prepared and cha-these molecular ribbons is primarily attributable to the enerracterized. Single-crystal X-ray structure analyses indicate getically more favourable syn conformation of both the that these ribbon-like molecules arrange in a folded confor-[3.3]metacyclophanes and the pyridinophanes. mation, with the pyridine and benzene units being folded inIn work published earlier we were able to show that ribbon-shaped molecules of type I, built up from The ribbon-shaped pyridine assemblies I are of interest because the integrated, complex-forming donor centres theyThe observed structures of such compounds may be due to a number of factors: the common tendency of many [3.3]metacyclophanes to arrange in a syn conformation, maximum packing in the crystal, and, as in the case of the self-assembly of folded proteins, the influence of the sidechains (tosyl in this case)L21.contain allow the complexation of cations and protons, which may solubilize compounds. We were also interested in ascertaining whether the ribbon-shaped molecules built from pyridine rings also undergo "self-assembly" leading to the folded structure described for their benzenoid counterparts. Ultimately, the open-chain tetrafunctionalized compounds I are intended to be converted by macrocyclization to tube-shaped molecules 11, which could serve as potential concave host compounds for guest ions and molecules [5].This work has shown that the methodologiesL61 developed for the syntheses of the ribbon-and belt-shaped (n)benzenophanes I, I1 may also be employed in the synthesis of analogous multiple pyridinophanes.We used diethyl 2,6-bis(bromomethyl)pyridine-3,5-dicarboxylate (1) as the basic building block, which can be considered as the pyridine analogue of diethyl 2,4-bis(bromomethy1)benzene-1,5-dicarboxylate['1. The mono sodium salt of 4-toluenesulfonic acid amide 2 and the amine 3 were chosen as the cyclization partners of 1 for the preparation of two-layered pyridino-or benzenopyridinophanes. Threelayered tetraaza-or tetrathiapyridinophanes were prepared by the reaction of 1 with the tetrakis(tosylaminomethy1) compound 4 or the tetrakis(mercaptomethy1) compound 5.

A Field Guide to Foldamers

“…Investigations into the construction of larger cyclophanes − proceeded through the generation of linear oligomers of tetrasubstituted aryl moieties linked through tosylated aminomethyl groups. Through iterative synthesis, chain lengths up to the nonamer 401 were obtained and crystal structures for pentamer 21 revealed stacked, molecular ribbons (Figure ).…”

“…Although detailed spectroscopic studies and folding transitions through either solvent or thermal denaturation were not demonstrated, these structures have similar conformations to previously described aedamers. In chloroform, 1 H NMR showed that the S-shaped folded conformation is the preorganized structure before cyclization to the macrocycles. , Extensions of this backbone have included the incorporation of p -phenyl rings, pyridines, and biphenyl groups, as well as the use of thioether linkages. , …”

“…Recently, longer chains with up to five aromatic rings suggest collapsed conformations in aqueous solution, with open conformations in chloroform. 396 Investigations into the construction of larger cyclophanes [397][398][399][400][401][402][403] proceeded through the generation of linear oligomers of tetrasubstituted aryl moieties linked through tosylated aminomethyl groups. Through iterative synthesis, chain lengths up to the nonamer 401 were obtained and crystal structures for pentamer 21 revealed stacked, molecular ribbons (Figure 63).…”

“…396 Investigations into the construction of larger cyclophanes [397][398][399][400][401][402][403] proceeded through the generation of linear oligomers of tetrasubstituted aryl moieties linked through tosylated aminomethyl groups. Through iterative synthesis, chain lengths up to the nonamer 401 were obtained and crystal structures for pentamer 21 revealed stacked, molecular ribbons (Figure 63). Although detailed spectroscopic studies and folding transitions through either solvent or thermal denaturation were not demonstrated, these structures have similar conformations to previously described aedamers.…”

Structure and Conformational Properties of three-layered Cyclophanes prepared by a one-pot Synthesis

“…However, a complex mixture was obtained after repeated trials. Thus, the reaction was then carried out under heterogeneous dilute conditions 13 at room temperature instead. A solution of 1 and 2 in a mixture of ethanol and benzene was stirred for 5 days at room temperature to give a separable mixture of the desired three-layered cyclophanes (Scheme 1).…”