C–C coupling between trinitrothiophenes and triaminobenzenes: zwitterionic intermediates and new all-conjugated structures

Abstract

The reactions of 1,3,5-triaminobenzene derivatives with 2,3,4-trinitrothiophene and 2-bromo-3,4,5-trinitrothiophene gave new all-conjugated compounds bearing both an electron-withdrawing and an electron-donor moiety on the same unit. The reactions with 2,3,4-trinitrothiophene offered evidence, by NMR spectroscopy at low temperature, of the formation of new labile Wheland-Meisenheimer intermediates whereas at room temperature stable unexpected products derived from the attack of the nucleophile at C-4 with replacement of the nitro group were isolated. Their formation caused, in turn, the obtainment of a salt between 1-nitroso-2,4,6-triaminobenzenes and 2,4-dinitrothiophen-3-ol. The reactions with 2-bromo-3,4,5-trinitrothiophene produced in good yields the SNAr substitution product with the displacement of the bromide. All the new coupling products obtained are of applicative interest, considering the increasing concern for highly conjugated π-systems in solar energy conversion or optoelectronic devices.

Nucleophile/Electrophile Combinations in Aromatic Substitution: From Wheland to Wheland–Meisenheimer Intermediates Using Strongly Activated Arenes

“…Scheme 20 Exchange of the electrophilic partner between two WM complexes A third kind of electrophile coupled with 1,3,5-triaminobenzenes 1-3 was 2,3,4-trinitrothiophene (22). 41 In this case only 1 and 3 showed the ability to attack, in a fast step, the unsubstituted carbon atom (C5) of the electrophile (Scheme 21). Species WM7 and WM8 were stable only at low temperature and were formed, detected, and characterized at -70 °C in CD 2 Cl 2 .…”

4,6-Dinitro-7-(thiazol-2-ylamino)benzo[c][1,2,5]oxadiazole 1-oxide

“…In the latter case, the reaction course has been studied with a wide number of substrates and, in many cases, the reaction intermediates have been detected and isolated. For a long time, we have been studying this kind of reaction, coupling strongly activated neutral aromatics such as 1,3,5-triaminobenzenes with a series of electrophiles, both charged and neutral [5][6][7][8].…”

3,5-Dimethoxy-2-[(4-methoxyphenyl)diazenyl]phenol

“…The principal method for the synthesis of azoic compounds is the azo-coupling reaction, a kind of electrophilic substitution reaction, that is one of the most important and versatile methodologies in organic synthesis [3,4]. From many years, we are studying aromatic substitution reaction, both electrophilic and nucleophilic, including azo-coupling reaction [5][6][7][8]. Now we report the synthesis, by azo-coupling reaction, of a novel azo compound, namely 3,5-dimethoxy-2-[(4-methoxyphenyl)diazenyl]phenol.…”