meso-Arylporpholactones and their Reduction Products

• Published in: Journal of organic chemistry Vol. 77; no. 15; pp. 6480 - 6494
• Main Authors: Brückner, Christian, Ogikubo, Junichi, McCarthy, Jason R, Akhigbe, Joshua, Hyland, Michael A, Daddario, Pedro, Worlinsky, Jill L, Zeller, Matthias, Engle, James T, Ziegler, Christopher J, Ranaghan, Matthew J, Sandberg, Megan N, Birge, Robert R
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 03.08.2012; Amer Chemical Soc
• Subjects: Chemical reactivity; Chemistry; Chemistry, Organic; chlorins; Crystallography, X-Ray; Exact sciences and technology; Heterocyclic compounds; Heterocyclic compounds with n hetero atom and also o and/or s, se, te hetero atoms; Heterocyclic compounds with only one n hetero atom and condensed derivatives; Heterocyclic compounds with several n hetero atoms in the same ring, in separated rings or in fused rings; Lactones - chemical synthesis; Lactones - chemistry; Lewis bases; Models, Molecular; moieties; Molecular Structure; optical properties; Organic chemistry; oxazoles; oxidation; Oxidation-Reduction; oxygen; Physical Sciences; Preparations and properties; Reactivity and mechanisms; Science & Technology; PRESSURE-SENSITIVE PAINT; PORPHYRIN CHEMISTRY; PHOTODYNAMIC THERAPY; CORE CONSTRUCTS; ORBITAL THEORY; CHLOROPHYLL ANALOG CHEMISTRY; PHOTOPHYSICAL PROPERTIES; SPARSELY SUBSTITUTED CHLORINS; SYNTHETIC ANALOGS; EXCITED-STATES; MO method; Molecular structure; Nitrogen heterocycle; Molecular interaction; Pyrrole derivatives; Chemical reduction; Steric effect; Optical properties; Chlorins; Oxidation; Chemical reactivity; Chemical synthesis; Oxazole derivatives; Chromophore; Oxygen nitrogen heterocycle; Permanganates; Electronic properties; Theoretical study; Stepwise mechanism; Ketone; X ray diffraction; Planar molecule; Valence; MNDO method; Porphyrin; Oscillator strength; Nucleophilic substitution; Porphyrin derivatives; Conformation; Nucleophile; Crystalline structure
• ISSN: 0022-3263; 1520-6904; 1520-6904
• DOI: 10.1021/jo300963m

The rational syntheses of meso-tetraaryl-3-oxo-2-oxaporphyrins 5, known as porpholactones, via MnO4 –-mediated oxidations of the corresponding meso-tetraaryl-2,3-dihydroxychlorins (7) is detailed. Since chlorin 7 is prepared from the parent porphyrin 1, this amounts to a 2-step replacement of a pyrrole moiety in 1 by an oxazolone moiety. The stepwise reduction of the porpholactone 5 results in the formation of chlorin analogues, meso-tetraaryl-3-hydroxy-2-oxachlorin (11) and meso-tetraaryl-2-oxachlorins (12). The reactivity of 11 with respect to nucleophilic substitution by O-, N-, and S-nucleophiles is described. The profound photophysical consequences of the formal replacement of a pyrrole with an oxazolone (porphyrin-like chromophore) or (substituted) oxazole moiety (chlorin-like chromophore with, for the parent oxazolochlorin 12, red-shifted Q x band with enhanced oscillator strengths) are detailed and rationalized on the basis of SAC–CI and MNDO-PSDCI molecular orbital theory calculations. The single crystal X-ray structures of the porpholactones point at a minor steric interaction between the carbonyl oxygen and the flanking phenyl group. The essentially planar structures of all chromophores in all oxidation states prove that the observed optical properties originate from the intrinsic electronic properties of the chromophores and are not subject to conformational modulation.