A series of hetero-azuliporphyrins have been prepared by the “3 + 1” variant on the MacDonald condensation. Azulitripyrranes with tert-butyl and phenyl substituents reacted with thiophene or selenophene dialdehydes in the presence of TFA to give, following an oxidation step, thia- and selena-azuliporphyrins in 45–55% yield. Two of these compounds gave crystals suitable for X-ray crystallographic analysis and the data were consistent with the presence of a 17-atom delocalization pathway. The hetero-azuliporphyrins have significant diatropic character that is enhanced by the presence of an electron-donating tert-butyl substituent. The aromatic character is further increased in polar solvents such as DMSO, which are believed to stabilize dipolar resonance contributors with 18π electron delocalization pathways. Protonation also greatly increases the diatropic characteristics of these macrocycles. The porphyrinoids underwent an oxidative ring contraction with t-BuOOH–KOH to give moderate yields of benzoheterocarbaporphyrins. Reaction of azulitripyrranes with 2,5-furandicarbaldehyde afforded oxa-azuliporphyrins, a class of carbaporphyrinoids that had previously been inaccessible. These “missing links” in the study of heteroazuliporphyrins were isolated as the dihydrochloride salts. Protonated oxa-azuliporphyrins are stable aromatic compounds, but the free base forms underwent rapid decomposition in solution.
通过麦克唐纳缩合的“3+1”变体制备了一系列杂珠脂
卟啉。具有叔丁基和苯基取代基的苯并
吡喃与
噻吩或
硒吩二醛在 TFA 存在下反应,经过氧化步骤,得到
硫杂-和
硒-苯并
卟啉,产率 45-55%。其中两种化合物产生适合 X 射线晶体学分析的晶体,并且数据与 17 原子离域路径的存在一致。杂朱脂
卟啉具有显着的变异性特征,这种特征通过给电子叔丁基取代基的存在而增强。在极性溶剂(例如
DMSO)中,芳香族特性进一步增强,人们认为它可以通过 18π 电子离域途径稳定偶极共振贡献者。质子化也大大增加了这些大环化合物的变异性特征。类
卟啉与 t-BuOOH-KOH 发生氧化环收缩,产生中等产量的苯并杂碳
卟啉。偶氮三
吡喃与
2,5-呋喃二甲醛反应得到氧杂偶氮
卟啉,这是一类以前无法获得的碳
卟啉类化合物。杂朱脂
卟啉研究中的这些“缺失环节”以二盐酸盐的形式被分离出来。质子化氧杂苯并
卟啉是稳定的芳香族化合物,但游离碱形式在溶液中会快速分解。