A Proton Dance: Wheland Complexes and Ammonium Salts Obtained from Organic Acids and 1,3,5-Tris(N,N-dialkylamino)benzene Derivatives

Ring Closure of Azo Compounds to 1,2-Annulated Benzimidazole Derivatives and Further Evidence of Reversibility of the Azo-Coupling Reaction

“…It should be noted that the reaction depicted in Scheme 5 is indirect evidence for the reversibility of the azo coupling reaction 3,4 and suggests that the benzimidazole so formed bears an azo moiety with the electron-withdrawing group. Scheme 6 shows a reasonable mechanistic pathway to explain the reaction in Scheme 5 which is consistent with previously reported observations.…”

“…Scheme 6 shows a reasonable mechanistic pathway to explain the reaction in Scheme 5 which is consistent with previously reported observations. 3,4 Due to the reversible character of the azo coupling reaction, the p-nitrobenzenediazonium salt 4a (E Mayr = −5.1) 9 is expelled from 7d and then reacts with a second molecule of 7d to replace its p-methoxybenzenediazo moiety (E Mayr = −8.4), 9 thus producing 4d and 7a, which is the precursor of 9a. We had previously determined that the benzenediazonium salt bearing the electron-donating group is replaced by the more powerful electrophile.…”

“…3,4 Contained in the older literature, benzenediazonium cations have generally not been considered strong electrophilic reagents. In the recent Mayr classification, they are considered very strong electrophilic reagents; for example, Mayr's electrophilicity parameter for the 4-nitrobenzenediazonium cation (E = −5.1) 9 is very close to that of 4,6-dinitrobenzofuroxan (E = −5.06), 10 a carbon neutral superelectrophile that, when coupled with triaminobenzenes 1−3, permitted us to characterize, for the first time, Wheland−Meisenheimer intermediates.…”

“…9-((4-Nitrophenyl)diazenyl)-6,8-di(piperidin-1-yl)-1,2,3,4-tetrahydrobenzo [4,5] 7,9-Dimorpholino-6-((4-nitrophenyl)diazenyl)-3,4-dihydro-1H-benzo [4,5] …”

C-C Coupling Reactions between Benzofurazan Derivatives and 1,3-Diaminobenzenes

“…The 1,3,5-triaminobenzene derivatives—first studied by the pioneer work of Effenberger [ 1 ]—belong to neutral electron-rich aromatic substrates and are able to react at the neutral carbon atom [ 1 , 2 ]. (These kinds of nucleophiles have been reported to react with a plethora of electrophiles, such as proton [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ], halogens [ 11 , 12 ], acyl- [ 13 , 14 , 15 ], alkyl- [ 16 ], and aryl-halides [ 17 ]. The coupling between 1,3,5-triaminobenzene of types A and B and aryl diazonium salts gave stable Wheland intermediates ( W ) by the azo-coupling reaction [ 18 ] ( Scheme 1 ), conversely to what is usually reported in the textbooks.…”