meso-arylporpholactones and their reduction products.
The rational syntheses of meso-tetraaryl-3-oxo-2-oxaporphyrins 5, known as porpholactones, via MnO(4)(-)-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.
Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060, USA. c.bruckner@uconn.edu
Christian
C
Brückner
Junichi
J
Ogikubo
Jason R
JR
McCarthy
Joshua
J
Akhigbe
Michael A
MA
Hyland
Pedro
P
Daddario
Jill L
JL
Worlinsky
Matthias
M
Zeller
James T
JT
Engle
Christopher J
CJ
Ziegler
Matthew J
MJ
Ranaghan
Megan N
MN
Sandberg
Robert R
RR
Birge
D018360:Crystallography, X-Ray; D007783:Lactones / Q000138:chemical synthesis* / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction
D007783:Lactones