Oxazolochlorins. 2. Intramolecular Cannizzaro Reaction of meso -Tetraphenylsecochlorin Bisaldehyde † (original) (raw)
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The breaking and mending of porphyrins: reductive coupling of secochlorin bisaldehydes
Tetrahedron Letters, 2012
The reaction of free base or Ni(II) complex secochlorin bisaldehydes 4H 2 and 4Ni regenerates the ultimate starting material of the bisaldehydes, meso-tetraphenylporphyrin 2H 2 and 2Ni, respectively. Depending on the reaction conditions employed (hydrazine hydrate in pyridine at reflux or hydrazine hydrate activated with sulfur in the presence of aqueous NaOH at ambient temperature), either porphyrin 2H 2 is formed together with known dihydroxymorpholinochlorin 9H 2 or known 2-hydroxychlorin 8H 2 . Two different reaction pathways for the hydrazine reaction can be derived, either involving the formation of a meso-tetraphenyl-1,4,5-triazepinoporphyrin that loses spontaneously N 2 or a Wolff-Kishner-type pathway that also involves an intramolecular aldol-type reaction. Neither reaction is synthetically useful but both highlight in an impressive fashion the high thermodynamic stability of porphyrins. They also bring the 'breaking and mending of porphyrin' strategy to its ultimate conclusion by regenerating the starting porphyrin.
Tetrahedron Letters, 2013
Reaction of diolchlorins-made from meso-tetraarylporphyrins by OsO 4 -mediated oxidation-with NaIO 4 on silica gel in the presence of a secondary amine or alcohol, followed by MnO 4 À -induced oxidation, leads to the replacement of a pyrroline b-carbon with oxygen to form a-substituted oxazolochlorin aminals or acetals, respectively. This two-step, one-pot reaction is a significant improvement over existing methods to prepare the oxazoline-based porphyrinoids. The number of steps is reduced from 5 to 2 and the overall yields more than doubled to 33-86%. The reaction also allows the preparation of oxazolochlorins carrying meso-substituents that are incompatible with existing methods. Lastly, the reaction further highlights the reactivity of morpholino-chlorins and provides further clues as to the mechanism of the intriguing carbon-to-oxygen atom swap reaction step in the current reaction, as well as in previously observed reactions.
Porphyrin Macrocycle Modification: Pyrrole Ring-Contracted or -Expanded Porphyrinoids
Molecules, 2016
In recent years, several synthetic strategies aiming at the peripheral functionalization of porphyrins were developed. Particularly interesting are those involving the modification of β-pyrrolic positions leading to pyrrole-modified porphyrins containing four-, five-, six-or seven-membered heterocycles. Azeteoporphyrins, porpholactones and morpholinoporphyrins are representative examples of such porphyrinoids. These porphyrin derivatives have recently gained an increasing interest due to their potential application in PDT, as multimodal imaging contrast agents, NIR-absorbing dyes, optical sensors for oxygen, cyanide, hypochlorite and pH, and in catalysis.
The Journal of Organic Chemistry, 2006
N-(Porphyrin-2-ylmethyl)glycine was synthesized and used as precursor of azomethine ylide, which was trapped with several dipolarophiles. The reaction of that azomethine ylide with dimethyl fumarate afforded the expected adduct. However, with 1,4-benzo-and 1,4-naphthoquinones only dehydrogenated adducts were isolated. Also, the reaction of that ylide with meso-tetrakis(pentafluorophenyl)porphyrin and tetraazaporphine allowed access to novel porphyrin-chlorin and porphyrin-tetraazachlorin dyads.
1,2,3]Triazolo[4,5-b]porphyrins: New Building Blocks for Porphyrinic Materials
Angewandte Chemie, 2006
There has been a strong interest in recent years in developing multiporphyrin arrays through covalent or noncovalent synthetic methodologies. The synthesis of porphyrinbased framework solids is also an active field. These multiporphyrinic systems are of interest because of their potential application in a range of areas, such as electronics, materials, catalysis, and medicine. In fact, porphyrins are one of the most attractive building blocks for supramolecular systems. They offer a variety of desirable features, such as rigid planar geometry, high stability, intense electronic absorption and emission, a small HOMO-LUMO energy gap, and the ability to tune their optical and redox properties by changing the metal center. During the past decade, various synthetic strategies have been developed to make multiporphyrin oligomers with linear, cyclic, and cross-linked geometries. An elegant and versatile method developed by Osuka and Shimidzu consists of a Ag I -promoted coupling reaction of meso-unsubstituted porphyrins. This method allows the preparation of porphyrin arrays in which the constituent porphyrins are connected directly at their meso positions without any extra linking atoms. By using this method, Osukas group prepared a wide range of covalently linked porphyrin arrays, including meso-meso-linked linear porphyrin arrays, two-dimensional windmill arrays, three-dimensional gridlike arrays, strapped meso-mesolinked diporphyrins, and cyclic arrays. Further oxidation of the meso-meso-linked porphyrin arrays under strong conditions (DDQ and Sc(OTf) 3 ) provides porphyrin tapes and sheets (DDQ = 2,3-dichloro-5,6-dicyano-1,4benzoquinone, OTf = trifluoromethanesulfonate). These fully conjugated porphyrin systems have planar structures and display drastically red-shifted absorption spectra that reach into the far-IR region, which reflects the extensive p conjugation over the molecules. Other very interesting linear, dendritic, and cyclic multiporphyrin systems, as well as organometallic porphyrin arrays have been published in recent years. All of these well-defined multiporphyrin arrangements are interesting for application such as molecular photonic and electronic wires. In particular, the cyclic porphyrin arrays are excellent light-harvesting antenna systems that mimic those found in the photosynthetic system. Herein we report the synthesis of the novel heterocyclic system [1,2,3]triazolo[4,5-b]porphyrin and its use in the preparation of porphyrinic dimers and pentamers. The 1,2,3triazoles are an important type of heterocyclic compounds and are being studied by many research groups because of their theoretical interest and synthetic usefulness. They also find numerous applications in industry, in medicine, and as agrochemicals. 1,2,3-Triazoles can be synthesized by many approaches; one method involves the reaction of sodium azide with alkenes bearing strongly electron-withdrawing substituents to afford N-unsubstituted 1H-1,2,3triazoles in good yields. We have considered a synthetic route involving the reaction of b-nitro-meso-tetraarylporphyrins with sodium azide; in these reactions the porphyrins should behave as nitroalkenes and the formation of triazoloporphyrins was anticipated. Indeed, the [1,2,3]triazolo[4,5b]porphyrins 2 were obtained in moderate to good yields from the reaction of nitroporphyrins 1 with NaN 3 . The alkylation and arylation of the triazole moiety allowed easy access to new porphyrinic materials with potentially interesting applications.
Chemistry at the porphyrin periphery
1999
The objective of this work was to synthesize novel aromatic compounds based on tetraphenylporphyrins. These compounds are potential photosensitizers for use in photodynamic therapy. Several approaches were employed towards this goal. Numerous tetraphenylporphyrins possessing a variety of substituents were synthesized, characterized and used as starting materials to prepare the analogous diol chlorins via the patented osmium tetroxide oxidation. Compounds possessing hydroxy, methoxy, alkyl and halogen substituents were prepared. Studies involving the syntheses of these variously substituted mesotetraphenyl-v/c-2,3-dihydroxy-2,3-chlorins and analysis of their in vitro biological test results are presented and discussed. A number of these compounds appear very promising, particularly diphenyl-2,3-dihydroxy-2,3-chlorin (125) which had an LD50 value of 0.0024 uJVI 450 times as potent as the commercially available standard Photofrin. Attempts to improve the oxidation reaction via the reve...
Organic Process Research & Development, 2006
Rational routes to synthetic porphyrins bearing distinct mesosubstituents have typically been implemented at modest scale (<1 g quantities). The A 3 B-porphyrin 5-(4-hydroxymethylphenyl)-10,15,20-trip -tolylporphinatozinc(II) (Zn-1) is required in multigram quantities for possible commercial use in information storage applications. The synthesis of Zn-1 has been carried out by reaction of 5-(4-hydroxymethylphenyl)dipyrromethane and the dicarbinol derived from 1,9-dip -toluoyl-5-p-tolyldipyrromethane. Four improvements have been made to the steps leading to the dipyrromethane and dipyrromethane-dicarbinol: (i) use of 50 equiv of pyrrole in the condensation of an aldehyde to give the dipyrromethane (versus 100 equiv previously), (ii) 1,9-diacylation of a dipyrromethane using the hindered Grignard reagent 2,6-dimethylphenylmagnesium bromide and p-toluoyl chloride to give the 1,9-diacyl versus 1-acyl products in >10:1 ratio (versus 4:1 using EtMgBr), (iii) isolation of the dibutyltin complex of the 1,9-diacyldipyrromethane from the crude reaction mixture by direct crystallization using methanol/methyl tert-butyl ether (MTBE) (versus silica chromatography), and (iv) reduction of the dibutyltin complex of the 1,9-diacyldipyrromethane (250 mM) with ∼10-15 mol equiv of NaBH 4 (versus 25 mM and 40 mol equiv). The procedures have been carried out with no chromatography at large scale, affording the dipyrromethane (31, 59, or 79 g), the dibutyltin complex of a 1,9-diacyldipyrromethane (361 g), and reduction of the latter (45 g). The porphyrin-forming reaction has been performed (25 mM reactants at 50-mmol scale, or 10 mM at 64-mmol scale) in a two-step process of condensation and oxidation to give the free base porphyrin 1 in 3.7-or 5.8-g quantities. Metalation with zinc acetate afforded Zn-1, which was isolated by direct crystallization. Taken together, the various improvements facilitate synthesis of the target porphyrin Zn-1 and may have broad applicability.
J. Chem. Soc., Perkin Trans. 1, 1998
3,4-Diarylpyrroles (1) have been directly prepared in 20-50% yield by the reaction of -nitrostyrenes with aqueous TiCl 3 in 1,4-dioxane. Pyrroles 1 were also prepared via Barton-Zard pyrrole synthesis using the reaction of -nitrostilbenes with ethyl isocyanoacetate followed by de-ethoxycarbonylation. 3,4-Diarylpyrroles have been converted into dodecaarylporphyrins by reaction with aromatic aldehydes. Various aryl groups are readily introduced at the periphery of porphyrins by this method. Phenyl substitution at any of the positions of pyrroles decreases E ox 1/2 , while E 1/2 red is almost unchanged. On the other hand, substitution of the 2-thienyl group affects both the HOMO and LUMO energies, and the UV-vis spectra of dodeca-2-thienylporphyrins (4f or 4i) are extremely red-shifted.