Pyridine containing macrocycle

To mimic the square-pyramidal coordination of iron bleomycin, a series of iron (Il)complexes with pyridine-containing macrocycles 4 was synthesized and used for the epoxidation of alkenes with H2O2 (Scheme 4) [35]. These macrocycles bear an aminopropyl pendant arm and in presence of poorly coordinating acids like triflic acid a reversible dissociation of the arm is possible and the catalytic active species is formed. These complexes perform well in alkene epoxidations (66-89% yield with 90-98% selectivity in 5 min at room temperature). Furthermore, recyclable terpyridines 5 lead to highly active Fe -complexes, which show good to excellent results (up to 96% yield) for the epoxidation with oxone at room temperature (Scheme 4) [36]. 

Scheme 3.6 Alkene epoxidation with a pyridine-containing macrocycle bearing a pendant arm.

Sharghi, H. Niknam, K. Pooyan, M. The halogen-mediated opening of epoxides in the presence of pyridine-containing macrocycles. Tetrahedron 2001, 57, 6057-6064. 

Gong and Gibb have reported a pyridine-containing macrocycle, 30 (R=H), in which anion binding could be improved via an appropriate choice of counter cation (Scheme 9.8) [85]. Initial experiments with the TBA salts of various anions revealed relatively low binding affinities, with the Ka values (JH NMRinCDCl3) ranging from... 

Examples of seven-coordination in pyridine-containing macrocycles have also been osberved. Thus the iron(TI) complexes [Fe(L)X,] xhLO (L = 126 X = halide or pseudohalide) are formed923 when the corresponding seven-coordinate iron(lll) complexes are reduced with aqueous sodium dithionite in the presence of excess NaX or by the direct template synthesis with 2,6-diacetylpyridine and the corresponding tetramine in the presence of iron(IJ). The triimine moiety gives rise to a strong... 

S. Taktak, W. Ye, A. M. Herrera, E. V. Rybak-Akimova, Synthesis and catalytic properties in olefin epoxidation of novel iron(ll) complexes with pyridine-containing macrocycles bearing an amino-propyl pendant arm, Inorg. Chem. 46 (2007) 2929. 

The novel preparation of 5-cyano[n](2,4)pyridinophane-6-ones [n = 6 (5%), 7 (11%), 8 (63%), 9 (71%)] was conducted by allowing cyanoacetatoamide to react with cycloalk-2-enones <05OBC638>. Pd-Catalyzed amination of either 3,5-dibromo- or 3,5-dichloropyridine with linear polyamines led to the formation of a new family of pyridine-containing macrocycles (e.g. 6) possessing an exo -oriented pyridine iV-atoms <05HCA1983>. The treatment of 3,5-... 

Moretto et al. reported the synthesis of the pyridine-containing macrocycles 411 and 412 by the cobalt-catalyzed hetero-[2 + 2 + 2]-cycloaddition of the diyne 409 with the nitrile 410 (Scheme 130).190c A high para-selectivity was obtained and 411 was produced as the major product. 

Pyridine-containing macrocycles via comediated [2 + 2 + 2] cycloadditions of a,o -bis-alkynes 07ARK(12)7. 

Figure 7.9 A bimacrocyclic pyridine can be constructed following three different approaches (a) a non-macrocyclic precursor is doubly cyclized to give the bimacrocycle, shown in the middle, or (b) it can be built up stepwise. The left retrosynthesis represents the bridging of a X and Y containing macrocycle by a pyridine bridge while the right retro-synthesis starts from a pyridine-containing macrocycle...

A mixed cyclothiophene including phenylene units was synthesized by Tobe et al. [423], Macrocycle 4.55 (Chart 1.56) was made, which includes four alternating 2,5-thienylene and 1,3-phenylene units and is similar in shape to cyclo [8]thiophene 4.31. The meto-branched phenylene units helped to form the macrocycle and reduced strain energy, but interrupted the overall conjugation. The synthesis of a corresponding pyridine-containing macrocycle 4.56 was attempted, but the ring-closure reactions of penta- and heptacyclic precursors failed [424]. 

Beer and coworkers have used pyridinium groups in the synthesis of anion-templated interlocked molecular species such as rotaxane 80. They observed that the yield of pyridine-containing macrocycle 81 was significantly improved in the presence of 3,5-bis-hexylamide-substituted pyridininm derivative 82 Cl, as shown in Scheme 14. This was attributed to favorable jt-tt stacking interactions between the electron-rich hydroquinone gronps of the precursor and the electron-poor pyridinium of 82 Cl. This inspired the analogous synthesis of 80 as depicted below. 

One direction for the development in this area is looking for more active and stable complex. In 2011, Hapke and coworkers prepared CpCo(H2C = CHSiMc3)2 complex and was found active in [2 + 2 + 2] cycloaddition reactions [26], The other direction is the exploration of applications. In 2005, Maryanoflf and coworkers applied [2 + 2 + 2] cycloaddition reaction in the preparation of macrocycles [27]. In the presence of CpCo(CO)2, pyridine containing macrocycles were prepared from long-chain a,cr-diyne and nitriles, cyanamides, or isocyanates (Scheme 3.11). The regioselectivity of these reactions was affected by the length and type of linker unit between the alkyne groups, as well as by certain stereoelectronic factors. 

Scheme 3.11 Co catalyzed synthesis of pyridine containing macrocycles.

The first targeted synthesis of a homothiacalixarene analogue was reported by Tsuge et al. in 1977. High dilution reaction of 2,6-bis(bromomethyl)pyridine 5 and dithiol 6 under basic conditions lead to a 51 % yield of pyridine-containing macrocycle 7 (Scheme 16.1) [5]. 

Beer et al. (492) recently reported the synthesis of a zinc-pyridine containing macrocycle 484 and cryptand 485, based on a pyrrole framework (Fig. 262). A crystallographic study of the former shows that the macrocyclic loop is significantly twisted, having the effect of reducing the cavity size, which may have a bearing on the anion-receptor properties of such species. 

Moretto, A.F., Zhang, H.-C. and Maryanoff, B.E. (2001) Synthesis of pyridine-containing macrocycles by cobalt-mediated trimerization of triply-bonded species. Journal of the American Chemical Society, 123(13), 3157-3158. 

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