Macrocycle tetrameric

The compounds [CymB(Pz)3]Tl (136) and [FcB(Pz)3]Tl show polymeric structures, with bridging B(Pz)3 fragments in the solid state. This is a result of unfavorable steric interaction between the substituent on boron and the hydrogen atoms on the pyrazolyl ring 5-position. The structure of [Cym B(Pz)3]Tl is somewhat related, but it adopts a macrocyclic tetrameric structure rather than a linear polymeric structure. Ligands with secondary donors on the backbone may form additional bonds to the thallium atom. For example, in [HB(3-(2-pyridyl)Pz)3]Tl, weak TF"N interactions between pyridyl nitrogens and the T1 atom have been observed. HB(3-(2-MeOC6Fl4)Pz)3]Tl features close intramolecular TF 0 interactions. ... 

Detailed conformational analysis of the macrocyclic tetrameric species formed by dimerization of the Zn-O-Zn-O square dimers and of their ZnPr2 adducts revealed the structural divergence of the homo- and... 

An intriguing application of Zincke processes occurred in Marazano s synthesis of dimeric, tetrameric, and even octameric pyridinium macrocycles, including cyclostellettamine B, a sponge-derived natural product. The same strategy produced a synthesis of haliclamine A (121, Scheme 8.4.41), a cytotoxic sponge metabolite. Intermediate 119, itself produced via a Zincke route, underwent an intramolecular Zincke reaction, providing macrocycle 120, which was reduced to the natural product. 

By reaction of 2-alkyl-4,6-dichloro-l,3,5-trimethylborazines (alkyl = methyl, ethyl, i-propyl) with bis(trimethylsilyl)amine the tetrameric borazine ring systems 4-6 are produced (Fig. 2) they can be purified by several successive vacuum sublimations (yields 4-60%). If the borazines carry n-propyl and tert-butyl groups in the 2-position or if methylbis(trimethylsilyl)amine is used to bridge the borazine molecules, the macrocyclic ring formation is inhibited [17, 18]. 

Fig. 3. Dimeric and tetrameric macrocyclic structures obtained from (diethylboryl)pyridines...

Attempts to prepare macrocyclic structures from a mixture of compounds 10 and 11 failed and only tetrameric (8) and dimeric (12) structures with a six-membered C2N2B2 heterocycle can be isolated (Fig. 3) [23]. 

Fig. 4. Tetrameric 13 and trimeric 14, 15 macrocyclic structures obtained from (3-aminophenyl)boronic acid derivatives...

As in the case of the tetrameric macrocycles discussed above, compounds 17 and 18 can be considered as porphyrinogen analogues or as heteroatom-bridged heteroaromatic calix[4]arene derivatives. The two different conformations observed for 17 and 18 have analogues in compounds 16 (Fig, 5) [15, 28-30],... 

The tetrameric macrocycle of 21 has Q-symmetry and its conformation is similar to that of 18 with one opposite pair of imidazole rings in the plane of the molecule, and the other pair perpendicular to it. In 22 all five imidazole rings are almost perpendicular to the molecular plane, so that a CH2CI2 molecule can be included in the cavity of the pentamer. Unfortunately, compounds 19-23 are unstable under influence of air and moisture [33]. 

Thereby, the presence of tertiary monophosphines is critical, because both polymeric (26) and cyclic tetrameric (24 and 25) complexes can be obtained depending on the phosphine added to the reaction mixture. Furthermore, with some of the phosphines rapid decomposition and deposition of metallic silver occurs. In the macrocyclic molecules 24 and 25 a pair of silver atoms is bridged by two bis(l-imidazolyl)borate moieties, with a transannular Ag Ag distance of 8.61 A for 24 and 8.89 A for 25. The conformations of 24 and 25 are... 

Fig. 20. Reaction of 2,6-pyridinedimethanol with arylboronic acids gives the tetrameric macrocycles 74 and 75. Dimeric compounds are known with silicon 76 and 77 and sulfur 78...

Hawthorne and co-workers have also produced a series of macrocyclic Lewis acid hosts called mercuracarborands (156, 157, and 158) (Fig. 84) with structures incorporating electron-withdrawing icosahedral carboranes and electrophilic mercury centers. They were synthesized by a kinetic halide ion template effect that afforded tetrameric cycles or cyclic trimers in the presence or absence of halide ion templates, respectively.163 These complexes, which can bind a variety of electron-rich guests, are ideal for catalytic and ion-sensing applications, as well as for the assembly of supramolecular architectures. 

The major components are series of homologous trimers, tetramers, and pentamers of the three acids 44-46, along with smaller quantities of dimers, hexamers, and heptamers. Furthermore, the secretion contains several isomers of each oligomer, furnishing a combinatorial library of several hundred macro-cyclic polyamines [51, 52]. Using repeated preparative HPLC fractionation, the most abundant trimeric, tetrameric and pentameric earliest-eluting compounds were isolated. One and two-dimensional H NMR spectroscopic analyses showed that these molecules were the symmetric macrocyclic lactones 48, 49, and 50 (m, n, o, p, q=7) derived from three, four or five units, respectively, of acid 46. Moreover, using preparative HPLC and NMR methods, various amide isomers, such as 53,54, and 55 (Fig. 9) were also isolated and characterized [51,52]. 

Another interesting example of a transacetalization is the tetramerization of 1,3-dioxane 228 to the macrocycle 229 (Equation 92). This cyclooligomerization was promoted by dry HCl in Et20 and the tetrameric product was formed in 59% yield <20000L4125>. 

A second experiment should prove that macromonocycles are actually the intermediate supramolecular templates in the course of catenane formation. Therefore macromonocycle 17 was reacted with 5 and 3, and the first [2]catenane 18 of the amide type consisting of two different macromonocycles was isolated (Figure 8). Unsymmetric catenanes like 18 can be identified unambiguously by mass spectrometry, because the corresponding tetrameric macromonocycle can not be formed in this reaction sequence. This confirms the presumption that catenation here proceeds via a macrocycle rather than via intertwining open chain units. 

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