An Efficient Oxidation of 1,4-Dihydropyridines Using Aqueoustert.-Butylhydroperoxide

Aromatization of Hantzsch 1,4-Dihydropyridines Using Barium Manganate

“…Several oxidizing agents and methods such as potassium permanganate, 2 solid supported pyridinium chlorochromate (PCC), 3 silica gel supported ferric nitrate, 4 nitric oxide, 5 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 6 bismuth nitrate, 7 manganes dioxide, 6 ceric ammonium nitrate, 8 tert-butylhydroperoxide, 9 clay supported cupric nitrate accompanied by ultrasound-promotion, 10 using the system HNO 3 /bentonite in the absence of solvent by ORDER…”

Aromatization of Hantzsch 1,4-Dihydropyridines with Urea-Hydrogen Peroxide/Maleic Anhydride

“…This is in agreement with the observation made by others [3,4,16,21] employing different oxidative conditions. Dealkylation of 4-alkyl-dihydropyridines containing normal alkyl substituents, which was observed during oxidation by reported methods, such as with iodobenzene diacetate [18] or tertbutylhydroproxide [12], did not occur under our conditions. 1,4-DHPs bearing alkenyl-or aryl substituents at C-4 furnished the corresponding pyridine derivatives ( Table 1).…”

“…Significant research has been carried out and many approaches have appeared for the aromatization of Hantzsch 1,4-dihydropyridines, such as oxidation with Tl(NO 3 ) 3 · 3 H 2 O [3], BaMnO 4 [4], photochemical reactions [5], KMnO 4 [6], solid supported pyridinium chlorochromate (PCC) [7], silica gel supported ferric nitrate [8], nitric oxide [9], MnO 2 [10], ceric ammonium nitrate (CAN) [11], tert-butylhydroproxide [12], clay supported cupric nitrate [13], Bi(NO 3 ) 3 [14], I 2 /MeOH [15], Zr(NO 3 ) 4 [16], tetrakis-pyridine cobalt(II) dichromate (TPCD) [17], iodobenzene diacetate [18], NaNO 2 /NaHSO 4 /SiO 2 [19], NaNO 2 /C 2 H 2 O 4 [20], 3-carboxypyridinium chlorochromate (CPCC) [21], K 2 S 2 O 8 /Co(NO 3 ) 2 [22] and RuCl 3 /O 2 [23]. In continuing our effort to find a milder and high-yielding oxidant for the Hantzsch 1,4-DHPs, herein we wish to report that urea-hydrogen peroxide (UHP) in combination with maleic anhydride (MA) can serve as a powerful oxidant for the aromatization of the Hantzsch 1,4-DHPs.…”

A simple, efficient, one‐pot three‐component domino synthesis of Hantzsch pyridines under solvent‐free condition

“…Additionally, dihydropyridines are often produced in a synthetic sequence and have to be oxidized to pyridines [12]. Numerous reagents and procedures have been recommended for this purpose, such as pyridinium chlorochromate (PCC) [13], N 2 O 4 complex of 18-crown-6 [14], tert-butylhydroperoxide [15], photochemical oxidation [16], vanadium(V) salts [17], and biomimetic catalyzed oxidation [18].…”