Lash Timothy D, Szymanski Joseph T, Ferrence Gregory M
Department of Chemistry, Illinois State University, Normal, Illinois 61790-4160, USA.
J Org Chem. 2007 Aug 17;72(17):6481-92. doi: 10.1021/jo070947k. Epub 2007 Jul 26.
A series of eight dimethoxybenziporphyrins were prepared in three steps from 1,3-dimethoxybenzene or 2,6-dimethoxytoluene. Dibromination, followed by lithium-halogen exchange and reaction with benzaldehyde gave dicarbinol intermediates. These reacted with pyrrole and aryl aldehydes in the presence of BF3.Et2O in chloroform, followed by oxidation with DDQ, to give the benziporphyrins in 15-25% yield. These compounds readily gave nickel(II) and palladium(II) organometallic derivatives and could be selectively reduced with sodium borohydride to give unstable benziphlorins. Regioselective oxidation with silver acetate afforded the related 22-acetoxybenziporphyrins in 52-64% yield. The dimethoxybenziporphyrins showed chemical shifts by proton NMR spectroscopy that were consistent with weakly diatropic macrocycles. However, addition of TFA gave dications that showed far more significant shifts that are attributed to the presence of a more substantial diatropic ring current. The internal CH for 11H2(2+) was observed at 3.5 ppm, but this effect was diminished for the 3-methylbenziporphyrins 12H2(2+) where this resonance appears at 4.7 ppm. Even in the absence of the methoxy substituents, the dication derived from tetraphenylbenziporphyrin 8H2(2+) shows an upfield shift for this resonance to 5.5 ppm. The dications of the 22-acetoxybenziporphyrins also show similar effects despite the presence of an internal ester moiety. These results demonstrate that a spectrum of diatropic character can manifest even in highly crowded benziporphyrin derivatives.
从1,3 - 二甲氧基苯或2,6 - 二甲氧基甲苯分三步制备了一系列八种二甲氧基苯并卟啉。二溴化反应，接着进行锂 - 卤素交换并与苯甲醛反应，得到二苄醇中间体。这些中间体在氯仿中BF₃·Et₂O存在下与吡咯和芳基醛反应，然后用DDQ氧化，以15 - 25%的产率得到苯并卟啉。这些化合物很容易生成镍(II)和钯(II)有机金属衍生物，并且可以用硼氢化钠选择性还原得到不稳定的苯并卟吩。用醋酸银进行区域选择性氧化，以52 - 64%的产率得到相关的22 - 乙酰氧基苯并卟啉。二甲氧基苯并卟啉通过质子核磁共振光谱显示的化学位移与弱反磁大环一致。然而，加入三氟乙酸会生成二价阳离子，其显示出更显著的位移，这归因于存在更强的反磁环电流。11H₂(2⁺)的内部CH在3.5 ppm处观察到，但对于3 - 甲基苯并卟啉12H₂(2⁺)，这种共振出现在4.7 ppm处，这种效应减弱。即使没有甲氧基取代基，由四苯基苯并卟啉8H₂(2⁺)衍生的二价阳离子对于该共振也显示出向高场位移至5.5 ppm。22 - 乙酰氧基苯并卟啉的二价阳离子尽管存在内部酯部分，也显示出类似的效应。这些结果表明，即使在高度拥挤的苯并卟啉衍生物中，也能表现出一系列的反磁特性。
