Voltammetric oxidation of Hantzsch 1,4-dihydropyridines in protic media: substituent effect on positions 3,4,5 of the heterocyclic ring

Hydrated ferric perchlorate, Fe(ClO4)3.XH2O in organic synthesis. A short review

“…The aromatization of 1,4-DHP is also one of the ubiquitous problems in organic chemistry, and several researchers have reported oxidation methods including chemical oxidation with ferric or cupric nitrates on a solid support [129], oxidation with ceric ammonium nitrate [130], ultrasound-promoted oxidation by clay-supported cupric nitrate [131], oxidation with pyridinium chlorochromate [132], oxidation with nitric acid [133] Scheme 23 [134], Mn(OAc) [131,135], voltammetric oxidation of 1,4-DHP in protic [136] and in aprotic media [137] and Pd/C in acetic acid [138]. Ferric perchlorate also oxidizes Hantzsch 1,4-DHPs in acetic acid [139e].…”

Electrochemical oxidation of 4-monoalkyl-substituted 1,4-dihydropyridines

“…A series of pharmaceuticals [5] has been developed based mainly on 4-arylsubstituted 1,4-dihydropyridines. Antioxidant properties have also been confirmed for the heterocycle itself in reactions with various radicals [6,7]. On the other hand study of the redox reaction of the dihydropyridine ring is also important for the reason that its oxidation is the main metabolism of dihydropyridines.…”

“…However the products of electrochemical oxidation of dihydropyridines 2, 3, and 5 contain both 4-substituted pyridines (2a, 3a, 5a) and also 4-unsubstituted pyridine (6). In addition to both oxidized forms, tetrahydropyridines 2b, 3b, 5b were isolated from the reaction mixture.…”

N,N'-Ethylene-bis(benzoylacetoniminato) Copper (II), Cu(C22H22N2O2), a New Reagent for Aromatization of Hantzsch 1,4-Dihydropyridines

“…Yields were obtained using GC analysis. All products were known compounds and their physical and spectroscopic data were compared with those of authentic samples [4,11,12,30,31] and found to be identical.…”

“…Early experiments mostly used strong oxidants, such as HNO 3 [7], KMnO 4 [8], cerium ammonium nitrate (CAN) [9] or I 2 -MeOH [10]. New more efficient and environmentally benign methods, such as electrochemical oxidation [11] and catalytic aerobic oxidation using RuCl 3 [12], Pd/C [13], activated carbon [14] or Fe(ClO 4 ) 3 [15] have also been reported.…”