Oxazolochlorins 21. Most Efficient Access to meso-Tetraphenyl- and meso-Tetrakis(pentafluorophenyl)porpholactones, and Their Zinc(II) and Platinum(II) Complexes

Abstract

meso-Phenyl- and meso-pentafluorophenyl-porpholactones, their metal complexes, as well as porphyrinoids directly derived from them are useful in a number of technical and biomedical applications, and more uses are expected to be discovered. About a dozen competing and complementary pathways toward their synthesis were reported. The suitability of the methods changes with the meso-aryl group and whether the free base or metal derivatives are sought. These circumstances make it hard for anyone outside of the field of synthetic porphyrin chemistry to ascertain which pathway is the best to produce which specific derivative. We report here on what we experimentally evaluated to be the most efficient pathways to generate the six key compounds from the commercially available porphyrins, meso-tetraphenylporphyrin (TPP) and meso-tetrakis(pentafluorophenyl)porphyrin (TFPP): free base meso-tetraphenylporpholactone (TPL) and meso-tetrakis(pentafluorophenyl)porpholactone (TFPL), and their platinum(II) and zinc(II) complexes TPLPt, TFPLPt, TPLZn, and TFPLZn, respectively. Detailed procedures are provided to make these intriguing molecules more readily available for their further study.

Metal Complexes of Porphyrinoids Containing Nonpyrrolic Heterocycles

“…p -Benziporphyrin derivatives, such as naphthiporphyrin and anthriporphyrin 118 , have also been synthesized along [3 + 1]-pathways and exhibiting parallels in their structure and metalation characteristics (Scheme ), while exhibiting the expected changes in their electronic properties that come with the presence of expanded π-systems. − …”

“…Thus, they have been efficiently prepared by oxidative conversion of porphyrins and hydroporphyrins, whereby numerous substrates and methods are suitable to affect this conversion (Scheme ). ,,− If the metalloporpholactones are desired, the metal ions can already be present in a metalloporphyrin/chlorin to be oxidized. Alternatively, metal insertion reactions into free-base porpholactones using standard methodologies for porphyrins are adequate to prepare a range of metal complexes. , …”

[3 + 2]-Cycloadditions with Porphyrin β,β′-Bonds: Theoretical Basis of the Counterintuitive meso-Aryl Group Influence on the Rates of Reaction

“…The observation that the β,β′-double bond of T F PP is more reactive than the corresponding bond(s) of TPP is also more general: (a) The oxidation of T F PP or other tetraarylporphyrins carrying electron-withdrawing phenyl substituents using RuO 4 (generated in situ) to generate the corresponding porpholactones are more high-yielding compared to the oxidation of TPP (or tetraarylporphyrins carrying electrondonating phenyl substituents); 6 (b) the oxidation of T F PP using MnO 4 − is also very facile (eventually generating, like the RuO 2 -mediated oxidations, porpholactones), 7 while TPP is inert under these conditions. 10 These findings are unexpected since oxidations are inherently electrophilic reactions that are expected to be more facile for electron-rich double bonds. This reactivity difference is presumably also the reason behind why the majority of other cycloaddition reactions have also been described using T F PP and not the cheaper and more readily available TPP.…”

meso-Tetrahexyl-7,8-dihydroxychlorin and Its Conversion to ß-Modified Derivatives

“…Its 1 H NMR indicated the presence of al pyrrole hydrogens, but the region corresponding to the most shielded CH2 group, the group closest to the ring, had become more complex, suggestive of the formation of three non-equivalent meso-hexyl groups, supporting its assignment as the 1'-oxohexy derivative 14. Evidently, the porphyrin ring activated the meso-hexyl group to allow fo an alkane CH oxidation, a reaction not ordinarily observed in DMP-mediated oxidations Over the years, we have developed the cetyltrimethylammonium permanganate (CTAP)-induced oxidation of meso-tetraarylporphyrins or meso-tetraaryldihydroxychlorins to form their corresponding porpholactones [67][68][69][70]. This conversion is complementary to a number of other oxidation reactions that form porpholactones [71][72][73][74][75].…”