Macrocycles pyridine-containing

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]. 

Bastida, R. de Bias, A. Castro, P. Fenton, D. E. Macias, A. Rial, R. Rodriguez, A. Rodriguez-Blas, T. Complexes of lanthanide(III) ions with macrocyclic ligands containing pyridine head units. J. Chem. Soc., Dalton Trans. 1996,1493-1497. 

Additions to the ring are also named. For example, in dicyclohexano-18-Crown-6 the macrocyclic ring contains ethylenic carbon atoms that are also a part of cyclohexane rings, while dibenzo-18-Crown-6 has benzene rings at the same positions. In pyridino-18-Crown-6, the nitrogen from a pyridine ring replaces one of the oxygens. 

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... 

While the majority of macrocycles formed by this type of Schiffbase condensation reaction are derived from pyridine containing fragments, considerable attention has also been devoted to the use of other heterocycles, including five membered ones, as the primary macrocyclic precursors. Although these latter ligands are for the most part not completely conjugated, they form an important group of expanded porphyrin-type macrocycles. It is for this reason that they are included in the present review,... 

The synthesis of the pyrrole-pyridine-containing expanded porphyrins 4.196 and 4.197 was reported by Bell, et al. in 1993. These macrocycles, termed torands because of their rigid torroidal structure, were prepared via an elaborate linear synthesis, part of which is shown in Scheme 4.6.4. The key macrocyclization step in the synthesis involves the pyrolysis of the bis(semicarbazone) 4.195 to afford torand 4.196 in up to 69% yield. This torand may then be dehydrogenated with... 

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...

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