1,3-Dioxopyrrolo[3,4-b]porphyrins: synthesis and chemistry

Aromaticity versus regioisomeric effect of β-substituents in porphyrinoids

Maximizing the regioisomeric effect of β-substituents on photophysical properties of porphyrinoids through disruption of TT-conjugation and reducing the aromaticity.

One-Pot Synthesis of Four Chlorin Derivatives by a Divergent Ylide

Chlorins have unique photophysical properties that are exploited in diverse biological and materials applications. De novo chlorin synthesis with specific exocyclic motifs can be challenging and many are not stable to photobleaching and/or oxidation. A facile approach to a stable synthetic chlorin with a fused N-methyl pyrrolidine uses cyclo addition of a sarcosine-based azomethine ylide on 5,10,15,20-tetrakis(2,3,4,5,6-pentafluorophenyl)-porphyrin (TPPF₂₀) is reported, but this approach has limitations. We report the synthesis of stable chlorin scaffolds starting with TPPF₂₀ using a new glycine-based N-(hydroxymethyl)- N-methelenemethanideaminium ylide. Careful control of the 1,3-dipolar cycloaddition reaction allows a divergent use of the glycine derived ylide to yield four new chlorins, including the fused NH-pyrrolidine, two dimers, and the same N-methyl chlorin product from the sarcosine ylide reaction. The mechanism begins with the formation of a bis(hydroxymethyl)glycine, which then dehydrates and decarboxylates to form the active N-(hydroxymethyl)- N-methelenemethanideaminium ylide, which then reacts with TPPF₂₀ to form a key N-(hydroxymethyl)-17,18-pyrrolidinyl-chlorin intermediate. Deformylation of this intermediate affords the (17,18-pyrrolidinyl)-chlorin, whereas a Cannizzaro-type reaction promotes a hydride attack to an imine chlorin cation to yield the N-methyl chlorin. The exocyclic NH-pyrrolidine provides a unique mode of attaching chiral moieties that avoids formation of diasteromers at the bridgehead carbons.

Facile synthesis of chlorin bioconjugates by a series of click reactions

A multifunctional chlorin platform appended with four short polyethylene glycols and a carboxylate-linker allows rapid conjugation to biotargeting motifs such as proteins and oligonucleotides. The stability and photophysical properties of the chlorin enable development of diagnostics, imaging, molecular tracking, and theranostics.

β-Formyl- and β-Vinylporphyrins: Magic Building Blocks for Novel Porphyrin Derivatives

Porphyrins bearing formyl or vinyl groups have been explored as starting materials to prepare new compounds with adequate features for different applications. In this review it is discussed mainly synthetic strategies based on the reaction of meso-tetraarylporphyrins bearing those groups at β-pyrrolic positions. The use of some of the obtained porphyrin derivatives for further transformations, namely via pericyclic reactions, is also highlighted.

Selective Vilsmeier–Haack aryl-formylations of tetrathienylporphyrin and its Ni(II) complex

Regioselective aryl-formylations of tetrathienylporphyrin and its Ni(II) complex were performed with the Vilsmeier–Haack reaction. We have studied different solvents and temperatures to obtain the mono, di, tri and tetra-formylated porphyrins, all at the α-position of the thienyl groups. No β-formylations were observed and the four different formylated products presented here are suitable intermediates for subsequent extended conjugation reactions.

New approach for post-functionalization of meso-formylporphyrins

An approach for the transformation of formyl groups into areneimidazoles at a porphyrin substrate is developed, allowing straightforward design of new polytopic porphyrinoid compounds.

meso-Tetraphenylbenzoporphyrin-2(2),2(3)-dicarboxylic anhydride: a platform to benzoporphyrin derivatives

A method to synthesize meso-tetraphenylbenzoporphyrin-2(2),2(3)-dicarboxylic anhydride is reported. This compound reacts with alkylamines and arylamines to afford the corresponding "phthalimides" in moderate to excellent yields. The reaction of the title compound with benzene-1,4-diamine or with benzene-1,3-diamine yields the corresponding N,N'-(phenylene)bisphthalimides, whereas with benzene-1,2-diamine or naphthalene-1,8-diamine it affords heterocyclic-fused porphyrins. Molecular mechanics simulations elucidates the multiplicity of signals observed in the NMR spectra of the N,N'-(1,4-phenylene)bisphthalimide 11. This molecule exhibits two preferential conformations corresponding to a coplanar and an almost perpendicular arrangement of the benzoporphyrin units relative to the central benzenic ring.

Steric bulkiness of pyrrole substituents and the out-of-plane deformations of porphyrins: nickel(II) octaisopropylporphyrin and its meso-nitro derivative

Sterically bulky substituents at the β-carbons of the pyrrole rings of porphyrins are sufficient to cause large out-of-plane porphyrin distortions even in the absence of substituent groups at the meso carbons. It is well established that substituents at the meso-positions only or at both the β-pyrrole and the meso-positions are sufficiently bulky to result in large non-planar distortions of the macrocycle. However, no systematic studies of the effects of bulky β-pyrrole substituents alone have been reported. Herein, molecular simulations and X-ray crystallography of nickel(II) 2,3,7,8,12,13,17,18-octa(isopropyl)porphyrin reveal that large out-of-plane distortions (>1.5 Å) are induced by the steric repulsion of the β-isopropyl groups but fail to lead to a single strongly energetically favored conformer. The molecular simulations indicate that multiple conformers differing in the orientation of the isopropyl groups and the macrocycle conformation coexist in solution and this is confirmed by resonance Raman spectroscopy. Large downshifts in the structure-sensitive lines result from the non-planar distortion, and line broadenings result from structural heterogeneity. The heterogeneity originates from tradeoffs between energy contributions from steric repulsion and macrocycle distortion. Simulations for 5-nitro-2,3,7,8,12,13,17,18-octa(isopropyl)porphyrin suggest two possible orientations of the nitro group with respect to the macrocycle mean plane — one nearly vertical (as in the crystal structure) and another that is nearly parallel. INDO/S semiempirical calculations indicate an orbital of the NO2 group resides between the porphyrin frontier orbitals with significant mixing of the nitro and porphyrin orbitals.KEYWORDS: porphyrin, non-planar, resonance Raman, X-ray crystallography, crystal structure, isopropyl, nitro, conformer, molecular mechanics, molecular simulations, density functional theory, steric crowding, conformational heterogeneity.