Nucleophilic Substitution of Hydrogen in Heterocyclic Chemistry

C-H Arylation of Nitroimidazoles and Nitropyrazoles Guided by the Electronic Effect of the Nitro Group

“…[PCy 3 H]BF 4 was purchased from Alfa Aesar and stored in a dessicator. 4-Nitroimidazole, 4-nitropyrazole, dimetridazole (8), and 1-butylimidazole (10) were purchased from TCI.…”

“…10 However, the high electrophilicity prevented from the use of strong bases for deprotonation of nitroazoles, thus limiting the synthetic utility of nitroazoles as nucleophiles. We envisioned that the presence of the nitro group should enable both the C5 positions of imidazoles and pyrazoles to be not only electrophilic but also the most acidic, allowing for efficient C-H functionalization reactions (Figure 1(d)).…”

A facile, metal-free, oxidative coupling of new 6-(hetero)aryl-[1,2,5]-oxadiazolo[3,4-b]pyrazines with pyrroles, indoles and carbazoles

“…The reactions proved to proceed as a classical nucleophilic aromatic substitution of hydrogen (SN H ) via the intermediacy of σ H -adducts, 5-(hetero)aryl-6-substituted-4,5-dihydro- [1,2,5]oxadiazolo [3,4-b]pyrazin-4-ium salts, and subsequent oxidation of these dihydro compounds by air oxygen (Scheme 3). While some pyrazine derivatives 10,[13][14][15][16][17] [3,4-b]pyrazine (1a) with pyrrole (7), indole (11), 1-ethyl-1H-indole (13) and carbazole (17) in the presence of various catalysts (Table 1). It has been established that the best yeild of the SN H -product derived from the reaction 1a with pyrroles is reached on using CF3COOH, whereas use of BF3·Et2O and CH3COOH leads to a complex multi-component mixture with a large amount of tar.…”

“…The optimal conditions, found for the reaction of 5-phenyl- [1,2,5]oxadiazolo [3,4-b]pyrazine (1a) with pyrroles, indoles and carbazoles, have been applied for the C-C coupling of 5-(hetero)aryl- [1,2,5]oxadiazolo [3,4-b]pyrazines (1b-d) with the same nucleophiles. Highly electrophilic azines (1a-d) have been found to react smoothly with pyrroles (7,8), indoles (11)(12)(13) and carbazoles (17)(18)(19) at room temperature to give the corresponding products 9-10, 14-16 and 20-22 in 71% , 87% and 76% yields, respectively. It is worth noting that structures of the SN Hproducts 9a, 10d, 14a, 21a, 22a and 22c have been established unequivocally by X-ray crystallography (Figs.…”

Synthesis, spectroscopic characterization and DFT calculations of a new highly fluorescent heterocyclic system: imidazo[4,5-a]quinindoline

“…24,25 The fluorescence properties of these new heterocyclic compounds and DFT calculations of one structure by using the B3LYP hybrid functional and the 6-311+G(d,p) basis set have also been studied.…”