Regiospecific naphthyl nitration of 5,10,15,20‐tetranaphthylporphyrin

Abstract

The nitration reaction of 5,10,15,20-tetranaphthylporphyrin (TNP) was investigated in detail and the mono-, di-, and tri-nitro-TNPs were synthesized in high yield using 65% HNO 3 . The 1 H-NMR study shows that the preferred site of nitration of the naphthyl substituted porphyrin is the carbon atom of the meso-substituents para to its bond to the porphyrin ring. The reaction leads to exquisite regioselectivity in favor of the mono, di, and tri-nitro-TNP. Quantumchemical ab initio calculations at different levels of theory were performed in order to explain the experimentally observed reactivity. RESULTS AND DISCUSSION Selective nitration of TNPCompared to the conventional nitration using fuming nitric acid [12] or NaNO 2 /TFA, [14] the reactions presented in this study proceeded smoothly at room temperature, under mild conditions with easy work-up procedures. Thus, after 0.7 mL 65% HNO 3 (yellow) was added to TNP (0.2 g) in 30 mL of CHCl 3 for about 20 min (monitored at intervals by TLC), 1 was obtained in high yield of 92%. General procedures for the synthesis of 2a, 2b, and 3 were exactly the same as that for 1 except that the reaction time was extended to 40 and 180 min, respectively. MS and TLC (wileyonlinelibrary.com)

Nitration of Porphyrin Systems: A Toolbox of Synthetic Methods

“…Porphyrins bearing aryl moieties in meso ‐positions (5, 10, 15, 20) can also be successfully nitrated in these rings. In this case, the only mechanism described in the literature was the electrophilic one [21,88–92,95–101,103] . For the first time, this type of nitration taking place on meso ‐phenyl rings was reported by Kruper et al [88] .…”

“…In 2018 a paper was published from our group in which the orientation of electrophilic nitration in free‐base meso ‐aryl substituted porphyrins was changed without complexation [37] . Contrary to the previous observations (substitution in meso ‐aryl rings, [21,88–92] described in the following Chapter 4 ), the reaction took place at position β . This was the case after introducing strong electron‐withdrawing groups, e. g .…”