Oxidation of meso-Diarylporphyrins by a Hypervalent Iodine Compound: Facile Synthesis of meso-Acyloxyporphyrins and Dioxoporphodimethenes

Abstract

Free-base meso-propanoyloxylated (–OCOEt) porphyrins and dioxoporphodimethenes (quinoid forms of dihydroxyporphyrins) were efficiently synthesized by the treatment of the corresponding meso-diarylporphyrins with PhI(OAc)2 in propionic acid. Basic hydrolysis of the obtained meso-mono- and -dipropanoyloxyporphyrins provided meso-hydroxyporphyrins (oxophlorins) and dioxoporphodimethenes, respectively. Reduction of the dioxoporphodimethenes generated unstable meso-dihydroxyporphyrins, and one-pot etherification of the meso-dihydroxyporphyrins yielded stable meso-dialkoxyporphyrins.

Nickel(II)meso‐Hydroxyporphyrin Complexes Revisited: Palladium‐Catalysed Synthesis, Electronic Structures of Derived Oxy Radicals, and Oxidative Coupling to a Dioxoporphodimethene Dyad

“…This compound was reported by Chen and co‐workers in 2009; they prepared it by iron(III) chloride oxidation of NiDPP . The free base dioxoDAP analogue was reported by Sugiura and co‐workers, who isolated it as a significant side product in the oxidation of H 2 DAP with excess PhI(OAc) 2 in propionic acid …”

“…We are confident from the 2D NMR analysis, that our blue product is the unusual 10 H ‐isooxophlorin and not the 15 H tautomer. The very narrow lines in the spectra of compound 15 c are remarkable, as the 1 H NMR spectrum of the free base DAP hydroxyporphyrin reported by Sugiura and co‐workers was “severely broadened”, perhaps due to the hydroxyporphyrin/oxophlorin tautomeric equilibrium.…”

“…In 2014, Lucas and co‐workers reported the formation of a 5‐hydroxytriarylporphyrin nickel(II) complex by anodic nucleophilic substitution of a nickel(II) triarylporphyrin; they also noted the difficulty of obtaining a 1 H NMR signal due to the presence of the oxy radical . Sugiura and co‐workers recently reported free base meso ‐hydroxyporphyrins derived from 5,15‐bis(3,5‐di‐ tert ‐butylphenyl)porphyrin (H 2 DAP); these were prepared by oxidation of the free base with PhI(OAc) 2 in hot propionic acid, followed by basic hydrolysis of the propionate esters . Although not closely relevant to our work on Ni II tetrapyrrole complexes, the recent report by Osuka and co‐workers on meso ‐hydroxysubporphyrin (that is, tripyrrolic) boron complexes is worth noting.…”

“…[13] Sugiuraa nd co-workers recently reported free base meso-hydroxyporphyrins derived from 5,15-bis(3,5-di-tert-butylphenyl)porphyrin (H 2 DAP);t hese were prepared by oxidation of the free base with PhI(OAc) 2 in hot propionic acid, followed by basic hydrolysis of the propionate esters. [14] Although not closely relevant to our work on Ni II tetrapyrrole complexes, the recent report by Osuka andc o-workers on meso-hydroxysubporphyrin (that is, tripyrrolic) boron complexes is worth noting. The authors were able to isolate and fully characterise the remarkably stable free oxy radical derived by autooxidation of a meso-hydroxys peciesw ith an axial phenylg roup on the central B III atom.…”

Synthesis, Optical Resolution, and Circularly Polarized Luminescence of an Axially Chiral Porphyrin Dimer

“…5,10‐Diarylporphyrin 2 as the important intermediate was prepared according to our previous report . The introduction of one acyloxy group was carried out by treatment with PhI(OAc) 2 in propionic acid . To avoid the formation of the bis‐acyloxy derivative that would decrease the yield of 5 , the reaction was monitored carefully.…”