Department of Chemistry, Illinois State University, Normal, Illinois 61790-4160, United States.
J Org Chem. 2011 Jul 15;76(14):5636-51. doi: 10.1021/jo200622s. Epub 2011 Jun 13.
Benziporphyrins, cross-conjugated porphyrin analogues with a benzene ring in place of one of the usual pyrrole units, have varying degrees of macrocyclic aromaticity because the 6π electron arene needs to give up its aromatic characteristics to facilitate conjugation over the entire system. As naphthalene would lose less resonance stabilization energy in giving up one of its benzene units, it was proposed that naphthiporphyrins would exhibit enhanced diatropicity compared to the related benziporphyrins. A naphthiporphyrin was prepared using the "3 + 1" variant of the MacDonald condensation by reacting 1,3-naphthalenedicarbaldehyde with a tripyrrane in the presence of TFA, followed by oxidation with DDQ. Although the free base form of naphthiporphyrin showed no overall diatropicity, the corresponding dication in TFA-CDCl(3) demonstrated a significant diatropic ring current where the internal CH shifted upfield to between 4.0 and 4.6 ppm. Naphthiporphyrin was converted to the corresponding palladium(II) complexes by reaction with Pd(OAc)(2) in acetonitrile, and the complex was further characterized by X-ray crystallography. Oxynaphthiporphyrins were similarly prepared by the "3 + 1" methodology from 4-methoxy-1,3-naphthalene-dicarbaldehyde, and these showed slightly enhanced diatropic character compared to oxybenziporphyrins. Reaction of oxybenziporphyrins or oxynaphthiporphyrins with silver(I) acetate afforded the corresponding silver(III) organometallic derivatives. A meso-tetraphenyl naphthiporphyrin was also synthesized in 4% yield by reacting a 1,4-naphthalene dicarbinol with 2 equiv of benzaldehyde and 3 equiv of pyrrole in the presence of BF(3).Et(2)O, followed by oxidation with DDQ. However, this 1,4-naphthiporphyrin showed reduced diatropic character compared to the corresponding p-benziporphyrin system. The NMR spectra for the 1,4-naphthiporphyrin show that the naphthalene unit pivots over the macrocycle and this presumably leads to further steric interactions that reduce the planarity of the macrocycle. These results demonstrate that while naphthiporphyrins can show enhanced aromatic properties as predicted, other factors may overwhelm this effect.
苯并卟啉是一种具有苯环取代吡咯单元的交叉共轭卟啉类似物，由于 6π 电子芳烃需要放弃其芳香特性以促进整个系统的共轭，因此具有不同程度的大环芳香性。由于萘在失去一个苯环单元时会失去更少的共振稳定能，因此有人提出，与相关的苯并卟啉相比，萘并卟啉将表现出增强的各向异性。通过在 TFA 存在下用三吡啶烷与 1,3-萘二醛反应，然后用 DDQ 氧化，使用 MacDonald 缩合的“3 + 1”变体制备了萘并卟啉。尽管萘并卟啉的游离碱形式没有表现出整体各向异性，但在 TFA-CDCl(3)中的相应二阳离子显示出显著的各向异性环电流，其中内部 CH 移向低场至 4.0 至 4.6 ppm 之间。通过在乙腈中与 Pd(OAc)(2)反应，将萘并卟啉转化为相应的钯 (II) 配合物，并用 X 射线晶体学进一步表征。通过“3 + 1”方法从 4-甲氧基-1,3-萘二醛制备类似的氧萘并卟啉，与氧苯并卟啉相比，这些氧萘并卟啉显示出略微增强的各向异性特征。用醋酸银 (I) 与氧苯并卟啉或氧萘并卟啉反应得到相应的银 (III) 有机金属衍生物。通过在 BF(3)。Et(2)O 存在下，用 2 当量的苯甲醛和 3 当量的吡咯与 1,4-萘二羧酸醇反应，以 4%的收率合成了一个中位四苯基萘并卟啉，然后用 DDQ 氧化。然而，与相应的 p-苯并卟啉体系相比，这种 1,4-萘并卟啉显示出降低的各向异性特征。1,4-萘并卟啉的 NMR 谱表明，萘单元在大环上旋转，这可能导致进一步的空间位阻相互作用，从而降低大环的平面性。这些结果表明，虽然萘并卟啉可以如预期的那样表现出增强的芳香性质，但其他因素可能会压倒这种影响。
