Sapphyrins

Sapphyrins were discovered serendipitously by Woodward33 during the course of synthetic studies directed towards the total synthesis of vitamin B, 2. The sapphyrins were the first example of expanded porphyrins in the literature. Due to sapphyrin exhibiting a deep-blue color in the crystalline state and intense green in solution. Woodward coined the expression sapphyrin with reference to the deep-blue color of sapphire stones. 

This experiment made clear that a [4 + 1] approach for the synthesis of sapphyrins is not very satisfactory. In further synthetic studies,33 Woodward demonstrated that sapphyrins could be obtained along different routes, but the yields of these methods were not at all satisfactory. 

Thus, small amounts of sapphyrins can be obtained via acid-catalyzed condensation between 3,4-dimethylpyrrole-2,5-dicarbaldchydc (51) and 3,4-dimethylpyrrole yielding the de-camethylsapphyrin 52. 

The parent unsubstituted sapphyrin is formed on condensation of bipyrroledicarbaldehyde 38 and dipyrrylmethanedicarboxylic acid 53. 

These experiments demonstrate that sapphyrins might be compounds of good stability, but that a rational approach is required to form sapphyrins in reasonable yields. 

Synthetic efforts in Woodward s33 and Johnson s311 laboratories were directed at the same time towards a [3 + 2]-McDonald strategy to make sapphyrins readily available. This approach was then used by others to synthesize different sapphyrins.le 15a,b 16,17... 

The approach makes use of a bipyrroledicarbaldehyde 54 and a tripyrranedicarboxylic acid 55 which are condensed with subsequent decarboxylation in the presence of acid and oxygen. The presence of oxygen, as in many other syntheses of porphinoid macrocycles, is necessary to adjust the oxidation level of the chromophore which is in sapphyrins a 2271-aromatic cyclically conjugated system. Many sapphyrins 56 with different substitution patterns have been synthesized according to this general scheme. As in all McDonald-type condensations at least one of the components has to be symmetric because otherwise mixtures of constitutional isomers would be formed. 

Following this procedure, optically active sapphyrin 58 can be obtained using the enantio-merically pure aldehyde (1./ )-(+ )-nopinone.19... 

Sandwich complexes nickel. 5, 35 Sapphyrins, 2, 888 demetallation, 2, 891 metallation, 2, 891 reactions, 2, 891 synthesis, 2, 889 Sarcoplasmic reticulum calcium/magnesium ATPase, 6, 566 skeletal muscle... 

Mn(phthalocyanine)(OCOH)(HC02H), 2, 866 MnC34H3SNs Mn(sapphyrin), 2, 889 MnC3 Hi9Ni0... 

The fe-Ir1 complex (344) of the selena sapphyrin ligand has been synthesized and characterized by X-ray diffraction studies.551 The pairs of bound N atoms in (344) are bent towards the Ir1 centers, and the respective pyrrole rings are twisted from the macrocyclic plane. The coordination geometry around the Ir is close to square-planar, and the Ir Ir distance is 4.233 A. The Se center is not involved in bonding to the Ir centers. 

The same strategy provides a useful tool to derivatize corrole 22 and sapphyrin 25 (Scheme 7). In the case of corrole 22, the reaction with pentacene (after 6 h at 200 °C) afforded mainly the dehydrogenated adduct 23 this is formed from the selective addition of pentacene to the befa-pyrrolic double bond near to the direct pyrrole-pyrrole link and subsequent dehydrogenation <04S 1291>. In minor amount, the reaction also gave rise to the dehydrogenated adduct 24 resulting from an unexpected thermal [4+4] cycloaddition reaction. 

In the reaction with sapphyrin 25, adduct 26 was produced with high selectivity (MW, 1 h, 200 °C), showing once again that the beta-pyrrolic double bond close to the pyrrole-pyrrole link contains the most reactive position of this type of macrocycle <06TL3131>. 

Scheme 7. DA reactions of corrole 22 and sapphyrin 25 with pentacene.

There are a limited number of fluorescent sensors for anion recognition. An outstanding example is the diprotonated form of hexadecyltetramethylsapphyrin (A-7) that contains a pentaaza macrocydic core (Figure 10.31) the selectivity for fluoride ion was indeed found to be very high in methanol (stability constant of the complex 105) with respect to chloride and bromide (stability constants < 102). Such selectivity can be explained by the fact that F (ionic radius 1.19 A) can be accommodated within the sapphyrin cavity to form a 1 1 complex with the anion in the plane of the sapphyrin, whereas Cl and Br are too big (ionic radii 1.67 and 1.82 A, respectively) and form out-of-plane ion-paired complexes. A two-fold enhancement of the fluorescent intensity is observed upon addition of fluoride. Such enhancement can be explained by the fact that the presence of F reduces the quenching due to coupling of the inner protons with the solvent. 

Expanded porphyrins (sapphyrins) in their protonated forms can bind anions such as phosphate and nucleotides, but no electrochemical investigations have been reported to date (Sessler et al., 1991,1992). 

Krai V, Davis J, Andrievsky A, Kralova J, Synytsya A, Pouckova P, Sessler JL (2002) Synthesis and biolocalization of water-soluble sapphyrins. J Med Chem 45 1073-1078. 

Anion Separation by Solid Support Bound Sapphyrins.131... 

Sapphyrin (e.g., 2) is the most venerable of the many expanded porphyrins now known. It was first discovered serendipitously in the Woodward group more than 30 years ago during the course of studies directed toward the synthesis of vitamin Recently improved syntheses of sapphyrin have been developed by the... 

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