Phenyl-substituted porphyrins: III. Relative reactivity in the nitration reaction

Abstract

Study on the nitration of phenyl-substituted porphyrins showed that protonation of the porphyrin macroring does not affect the relative reactivity of the meso-and β-positions and phenyl groups. * For communication II, see [1].Like other aromatic compounds possessing a closed conjugated π-electron system, porphyrins are capable of reacting with electrophiles to give the corresponding substitution products. The most interesting and widely known electrophilic substitution reaction is nitration. Nitration of compounds of the porphyrin series was reported for the first time in [2][3][4]. As a result, mesonitro derivatives were isolated even in reactions with porphyrins having no substituents in the β-positions. Treatment of porphyrin (I) with a nitrating mixture gives meso-nitroporphyrin (II), and further nitration of the latter yields 5,10-dinitroporphyrin (III) [5]. A mixture of meso-nitro derivatives V-VIII was obtained by nitration of octaethylporphyrin IV [6,7]. First attempts to perform electrophilic nitration of meso-tetraphenylporphyrin IX were unsuccessful. Treatment of IX with a nitrating mixture over a period of 9.5 h resulted in the formation of dihydroxyporphodimethene X, presumably through intermediate ipso-nitration product XI [8] (Scheme 1). Kruper et al. [9] succeeded in nitrating compound IX by treatment of its solution in methylene chloride or chloroform with fuming nitric acid (d = 1.53 g/cm 3 ). The nitration occurred at the para-position of one of phenyl substituents and afforded 5-(4-nitrophenyl)-10,15,20-triphenylporphyrin (XII) (Scheme 2). Further nitration (by increasing the amount of nitrating agent) led to the formation of a 2 : 1 mixture of isomeric 5,10-and 5,15-bis(4-nitrophenyl)-porphyrins XIII and XIV. Prolonged nitration gave 5,10,15-tris(4-nitrophenyl)-20-phenylporphyrin (XV). The nitration of compound IX and its derivatives with various nitrating agents was studied in detail in [10][11][12]. On the basis of the obtained results it was concluded that meso-and β-positions in meso-phenylporphyrins are deactivated toward electrophilic substitution owing to protonation of the inner nitrogen atoms [12]. Compound XVI was not isolated.The goal of the present study was to compare the reactivity of the meso-and β-positions in the porphyrin

Nitration of Porphyrin Systems: A Toolbox of Synthetic Methods

“…Nitration of porphyrins in meso ‐positions via electrophilic aromatic substitution using sodium nitrite was widely studied by Syrbu and Kolodina [54] . When 2,8,12,18‐tetraethyl‐3,7,13,17‐tetramethyl‐5,15‐diphenylporphyrin ( 45 ) was subjected to this reaction (in acetic acid, 1–2 h), the dinitro‐derivative 46 was obtained (88%).…”

“…Prolonging of the reaction time up to 4 days leads to trinitro‐derivative 47 bearing an additional NO 2 group on one of its phenyl rings (with 57% yield; Scheme 18). [54] It is worth mentioning that the nitro group first attaches to the unsubstituted meso ‐positions, then goes to a phenyl ring (only in the case when all the meso ‐positions are already occupied).…”

Phenyl Substituted Porphyrins. 6. Acylation of Alcohols with Carboxyphenylporphyrins

“…A two-step one-pot procedure analogous to [16][17][18] was employed to afford carboxyporphyrins 14 by the condensation of biladiene 12 with benzaldehydes 2 (X = -; R = Н and X = OCH 2 ; R = Et) in butanol and further hydrolysis of the obtained esters 13 (X = -; R = Ме and X = OCH 2 ; R = Bu). The yields were 20.8 % and 45.6 %, correspondingly (Scheme 4).…”

Phenyl Substituted Porphyrins. Part 5. Acylation of Aminophenylporphyrins

“…5-(4-Nitrophenyl)-10,15,20-triphenylporphyrin (1, 4-NO 2 ) was also obtained by nitration of meso-tetraphenylporphyrin 2 (side product of the "mixed aldehyde" condensation) with sodium nitrite in trifluoroacetic acid, similarly to [29,30] (Scheme 2), with subsequent reduction, which afforded significantly increased total yield of aminophenylporphyrin 5 (4-NH 2 ).…”