Porphyrins formyl

An example of an intermolecular aldol type condensation, which works only under acidic catalysis is the Knoevenagel condensation of a sterically hindered aldehyde group in a formyl-porphyrin with a malonic ester (J.-H. Fuhrhop, 1976). Self-condensations of the components do not occur, because the ester groups of malonic esters are not electrophilic enough, and because the porphyrin-carboxaldehyde cannot form enolates. 

A mild procedure which does not involve strong adds, has to be used in the synthesis of pure isomers of unsymmetrically substituted porphyrins from dipyrromethanes. The best procedure having been applied, e.g. in unequivocal syntheses of uroporphyrins II, III, and IV (see p. 251f.), is the condensation of 5,5 -diformyldipyrromethanes with 5,5 -unsubstituted dipyrromethanes in a very dilute solution of hydriodic add in acetic acid (A.H. Jackson, 1973). The electron-withdrawing formyl groups disfavor protonation of the pyrrole and therefore isomerization. The porphodimethene that is formed during short reaction times isomerizes only very slowly, since the pyrrole units are part of a dipyrromethene chromophore (see below). Furthermore, it can be oxidized immediately after its synthesis to give stable porphyrins. 

Of great importance for porphyrin chemistry is the introduction of carbon substituents by Vilsmeier formylation100 or Friedel-Crafts acylation.100 The introduced substituents allow further carbon-chain elongations and other transformations so that interesting porphyrin derivatives can be synthesized. The Vilsmeier formylation of copper octaethylporphyrin (5) takes place at themethine position. The copper can then be easily removed by treatment with acid.105... 

Finally, the isoporphyrins with a nitrogen atom inverted from the inner core into a /5-pyrrolic position can be prepared by classical porphyrin synthetic routes when the pyrrolelinking CH2X or formyl group is attached to the /J-position of the pyrrole subunit instead of the a-position of the pyrrole as in the synthesis of regular porphyrins. 

A key step proposed in the radical chain mechanism for the formation of the formyl complex is the coordination of CO to the Rh(OEP)- monomer, to give an intermediate carbonyl complex, Rh(OEP)(CO)- which then abstracts hydride from Rh(OEP)H to give the formyl product.This mechanism was proposed without direct evidence for the CO complex, and since then, again from the research group of Wayland, various Rh(fl) porphyrin CO complexes, Rh(Por)(CO), have been observed spectroscopically along with further reaction products which include bridging carbonyl and diketonate complexes. 

One step of the mechanism determined for the reaction of Rh(OEP)H with CO to give the formyl complex Rh(OEP)CHO involved the coordination of CO to the chain-carrying Rh(ll) porphyrin Rh(OEP)-, although there had been no direct evidence observed for this species.Since that time. Wayland has systematically developed the chemistry of Rh( 11) porphyrins coordinated to CO, and the chemistry is now well understood. 

In 1995, Boyd and co-workers <95TL7971 > covalently linked a porphyrin to fullerene Cgo through a 1,3-dipolar cycloaddition reaction involving the porphyrinic azomethine ylide 28 (Scheme 8). The ylide was generated in situ from befa-formyl-meso-tetraphenylporphyrin 27 and A -methylglycine, and provided the porphyrin-C6o diad 29 in good yield. 

Based on studies showing that the close proximity between the porphyrin and the Cm is essential for the observation of an electron transfer process, Fukuzumi and co-workers have prepared the porphyrin-C6o diad 41, in which the C6o-pyrrolidinyl moiety is directly connected to the meso position of the porphyrin macrocycle (Scheme 12) <03JPC(A)8834>. The strategy adopted for the synthesis of the starting porphyrin involved the 2+2 condensation of a maso-unsubstituted dipyrrylmethane with 3,5-di-tert-butylphenyl-substituted dipyrrylmethane and 3,5-di-tert-butylbenzaldehyde, to give 39, in 11.5% yield. Subsequent Ni(II) metallation, followed by Vilsmeier-Haack formylation and demetallation, gave rise to 40 which was used as the 1,3-dipole precursor this dipole in the presence of N-methylglycine and C6o, yielded the expected diad 41. 

D Ambrosio, M. GuerriCTO, A. Dd)itus, C. Ribes, O. Pi a, F. (1993) On the novel free porphyrins corallistin B, C, D, and E. Isolation from the demosponge Corallisles sp. of the Coral Sea and reactivity of their nickel(II) complexes toward formylating agents. Helv. Chim. Acta, 76, 1489-96. 

Formyl-5,10,15,20-tetraphenyl-porphyrin kann mit Nitro-methan zum Nitro-alken I, Nitro-alkohol II bzw. zum Bis-[nitromethyl]-Derivat III reagieren3 ... 

Magnesium, 3-[(17S)-7-formyl-8-ethyl-132-methoxy-carbonyl-2,12,18t-trimethyl-13 oxo-S-vinyl-W. 132,17,18-tetrahydro-cyclopenta[at]-porphyrin-17r-yl]-propionato-[(7R,1 lR)-trans-phytylester]... 

Though most non-experts are familiar only with the major chlorophylls of the plant world, chlorophyll a (25) and chlorophyll b (26) (which normally co-exist in approximately a 3 to 1 ratio), there exists a tremendous variety of other, less abundant, chlorophylls and bacteriochlorophylls. Chlorophyll c is found in certain marine algae, brown seaweeds and fresh water diatoms, but never in terrestrial life forms, and consists of a mixture of the two porphyrin acrylates (27) and (28). Certain species of Rhodophyceae possess chlorophyll d (29) and this pigment resembles chlorophyll a (25), except that the 3-vinyl in the latter is a formyl group in (29). 

Irreversible degradation of the porphyrin nucleus can be accomplished with oxidants such as chromium trioxide or potassium permanganate. As shown in Scheme 3, the products from the Cr03 reaction are maleimides, and this procedure has been used extensively for structure elucidation, and for tracking down the fate of isotopic labels in biosynthetic studies (B-75MI30702). In the absence of side chains such as formyl and vinyl, which are labile towards Cr03, it is possible to identify the various substituents on porphyrin subunits. 

Acetylation and formylation are classical reactions in porphyrin chemistry. H. Fischer s synthesis of hemin, for which he was awarded the 1930 Nobel prize, required treatment of deuterohemin (49) with acetic anhydride (or acetyl chloride) in the presence of tin(IV) chloride as a Friedel-Crafts catalyst the product, 3,8-diacetyldeuterohemin-IX (50), was obtained in high yield. Fischer also accomplished formylation of iron porphyrins using dichloromethyl methyl ether and a Friedel-Crafts catalyst (B-37MI30700). Both of Fischer s examples resulted in peripheral substitution of unsubstituted iron porphyrins. However,... 

Condensation of 5,5 -diunsubstituted dipyrrylmethanes (210) with one mole of a 2-formyl-5-methylpyrrole (211) affords high yields of tripyrroles (212), apparently uncontaminated with by-products due to reaction of the pyrrole at both ends of (210). The tripyrrole intermediates can then be reacted with a different formylpyrrole (213) to give the appropriate a,c-biladiene (214) cyclization then gives good yields of porphyrins (215) (Scheme 15) (73DOK(210)1090>. 

Hz IR (cm-1, nujol) iv=o 1700 cm-1). An X-ray crystal structure has confirmed the Rh(OEP)(CHO) structure. The porphyrin ligand clearly imparts special properties (stability, H NMR, IR) to the formyl ligand. However, the reason why the carbonylation of Rh(OEP)(H) should be more facile than the carbonylation of other metal hydrides is not yet apparent. 

The structure, function and organization of chlorophyll are well reviewed.370 272 At one time chlorophyll was thought to be present as a or b, b having a formyl group present at position 3 rather than a methyl group. However, chlorophylls c, d, c, and c2 are now known. The last two examples involve porphyrins rather than chlorins. 

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