An efficient, metal-free, room temperature aromatization of Hantzsch-1,4-dihydropyridines with urea–hydrogen peroxide adduct, catalyzed by molecular iodine

Oxidative Aromatization of Hantzsch 1,4-Dihydropyridines by H2O2/V2O5at Room Temperature

“…In this context, a wide variety of oxidants have been reported for the aromatization of Hantzsch 1,4-dihydropyridines such as ferric chloride hexahydrate, [1] manganese dioxde, [2] I 2 =MeOH, [3] nitrosoglutathione (GSNO), [4] silica chromate, [5] Zr(NO 3 ) 4 , [6] CO(NH 2 ) 2 Á H 2 O 2 =I 2 , [7] IBX, [8] ferric perchlorate, [9] oxone, [10] Pt (II) complex=hn, [11] 9-phenyl-10-methylacridinium=O 2 =hn, [12] NHPI=O 2 , [13] [14] vanadium(V) salts under microwave irradiation, [15] Pd=C=acetic acid, [16] and 2,6-dicarboxypyridinum. [17] However, most of these reactions require extended reaction time for completion and give poor yields of the products.…”

In situ formed tert-butyl hypoiodite as an efficient oxidant for rapid, room temperature, metal-free aromatization of Biginelli 3,4-dihydropyrimidin-2(1H)-ones under basic conditions

“…34 Under normal conditions or under ultrasound irradiation, molecular iodine selectively oxidizes 1,4-DHPs at elevated temperatures, 35 while in combination with the urea-hydrogen peroxide adduct (UHP), the same reaction is performed at room temperature. 36 In the case of 3,4-DHPMs, the UHP itself and in combination with molecular iodine, under different reaction conditions, did not afford a product with a satisfactory result. < 10%).…”

Graphite oxide-promoted one-pot synthesis and oxidative aromatization of Hantzsch 1,4-dihydropyridines

“…1 H NMR spectra were recorded on a Bruker 80 MHz in DMSO-d 6 using tetramethylsilane as internal standard. 13 C NMR spectra were recorded on a Bruker 62.9 or 100 MHz in DMSO-d 6 . Mass spectra were obtained on a FISONS GC 8000/TRIO 1000 under 70 eV.…”

“…Aromatization of 1,4-dihydropyridines (1,4-DHP) has been a focus of considerable attention from researchers in recent years, essentially since the discovery that the metabolism of those drugs involves an oxidation step that is catalyzed, in the liver, by cytochrome P-450 [8][9][10][11]. Several methods have been utilized for this oxidative conversion such as iodine [12], urea-hydrogen peroxide catalyzed by molecular iodine [13], peroxydisulfate-Co(II) [14], Conaphthenate [15], KBrO 3 /SnCl 4 Á5H 2 O [16], MnO 2 [17], silica-modified sulfuric acid/NaNO 2 [18], silica-sulfuric acid and Al(NO 3 ) 3 Á9H 2 O or Fe(NO 3 ) 3 Á9H 2 O [19], silicachromate [20], tetrakis(pyridine)cobalt(II) dichromate [21], b-cyclodextrin [22], electrochemical catalysis [23], and photochemical reaction [24]. It should be noted that for the above methods, 1,4-dihydropyridines are first prepared and then oxidized.…”