Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060, USA.
J Org Chem. 2012 Aug 3;77(15):6480-94. doi: 10.1021/jo300963m. Epub 2012 Jul 19.
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.
介孔四芳基-3-氧代-2-氧杂卟啉 5（称为卟啉内酯）的合理合成，是通过 MnO(4)(-)介导的相应介孔四芳基-2,3-二羟基氯（7）的氧化来实现的。由于氯 7 是从母体卟啉 1 制备的，这相当于用噁唑酮取代 1 中的一个吡咯部分。卟啉内酯 5 的逐步还原导致形成氯仿类似物，介孔四芳基-3-羟基-2-氧杂氯（11）和介孔四芳基-2-氧杂氯（12）。描述了 11 与 O、N 和 S 亲核试剂的亲核取代反应的活性。详细描述并基于 SAC-CI 和 MNDO-PSDCI 分子轨道理论计算，合理地解释了用噁唑酮（卟啉类发色团）或（取代）恶唑取代吡咯（氯仿类发色团，对于母体恶唑氯 12，Q(x) 带红移，振子强度增强）所带来的深刻光物理后果。卟啉内酯的单晶 X 射线结构表明，羰基氧与相邻的苯基之间存在较小的空间相互作用。所有氧化态下所有发色团的基本平面结构证明，观察到的光学性质源自发色团的固有电子性质，不受构象调制的影响。
