Pushpan S K, Srinivasan A, Anand V R, Chandrashekar T K, Subramanian A, Roy R, Sugiura K, Sakata Y
Department of Chemistry, Indian Institute of Technology, Kanpur-208-016, India.
J Org Chem. 2001 Jan 12;66(1):153-61. doi: 10.1021/jo001209y.
Synthesis and characterization of inverted porphyrins containing S, Se, and O are reported. A simple 3 + 1 MacDonald-type condensation using modified tripyrrane containing the N-confused ring and diols afforded various N-confused porphyrins 6a-f in 19-30% yield. The single-crystal X-ray structure of 6b shows a ruffled conformation with tilt angles of 21.11 degrees and 31.23 degrees for the N-confused ring and the adjacent pyrrole ring III, respectively, revealing its severe nonplanarity. Significant changes in C alpha-C beta, C beta-C beta, and C alpha-X bond lengths are observed in 6b relative to free thiophene and pyrrole, suggesting the altered delocalization pathway in the modified N-confused porphyrins. The two molecules in the unit cell show a cyclophane-type noncovalent dimer with a face to face orientation of two N-confused pyrrole rings as a result of the presence of weak N-H...N and C-H...N intermolecular hydrogen bonds involving pyrrole-NH, the N atom of the N-confused ring, and the C atom of the pyrrole ring. A detailed 1H and 13C NMR study by 1D and 2D methods allowed assignments of all the peaks in the free base and protonated forms. NMR studies reveal the presence of three different tautomeric forms in solution for 6c in CDCl3 at low temperature. UV-visible studies reveal absorption band shifts upon heteroatom substitution, and the magnitudes of these shifts are dependent on the nature of the heteroatom. In all cases both monoprotonated and diprotonated species have been identified, and on addition of acid, the first proton goes to the outer N2 atom of the N-confused ring.
报道了含硫、硒和氧的反式卟啉的合成与表征。使用含N-稠环的修饰三吡咯和二醇进行简单的3 + 1麦克唐纳型缩合反应，以19 - 30%的产率得到了各种N-稠卟啉6a - f。6b的单晶X射线结构显示出一种褶皱构象，N-稠环和相邻的吡咯环III的倾斜角分别为21.11度和31.23度，表明其具有严重的非平面性。相对于游离噻吩和吡咯，在6b中观察到Cα - Cβ、Cβ - Cβ和Cα - X键长有显著变化，这表明修饰后的N-稠卟啉中离域途径发生了改变。由于存在涉及吡咯 - NH、N-稠环的N原子和吡咯环的C原子的弱N - H...N和C - H...N分子间氢键，晶胞中的两个分子形成了一种环番型非共价二聚体，其中两个N-稠吡咯环面对面排列。通过一维和二维方法进行的详细的1H和13C NMR研究确定了游离碱形式和质子化形式中所有峰的归属。NMR研究表明，在低温下，6c在CDCl3溶液中存在三种不同的互变异构形式。紫外 - 可见研究表明，杂原子取代后吸收带发生位移，且这些位移的大小取决于杂原子的性质。在所有情况下，均已鉴定出单质子化和双质子化物种，加入酸后，第一个质子会加到N-稠环的外部N2原子上。
