Oxidation of 1,4-Dihydropyridines under Mild and Heterogeneous Conditions

Solvent‐Free One‐Pot Synthesis of Amidoalkyl Naphthols Catalyzed by Silica Sulfuric Acid

“…-There is current and general interest in heterogeneous systems because of their importance in industry and in the development of new technologies [1]. Heterogeneous-reagent systems have many advantages such as simple experimental procedures, mild reaction conditions, and minimum chemical wastes, when compared to analogous liquid-phase reactions [2]. Solid acid catalysts are easier to handle because they hold the acidity internally and are easily separated from products by simple filtration.…”

“…Amidoalkyl naphthols have been prepared with para-toluenesulfonic acid (TsOH), Bi(OTf) 3 , Zn(OTf) 2 , methanesulfonic acid (MsOH) [9], or iodine [10] as catalysts in organic solvents, elevated temperatures and prolonged reaction times often being required.…”

An Efficient Procedure for Deprotection of Acetals under Mild and Heterogeneous Conditions

“…16 Very recently, we among many others have demonstrated that heterogeneous reagent systems have many advantages such as simple experimental procedures, mild reaction conditions and minimization of chemical wastes as compared to the liquid phase counterparts. [23][24][25][26][27] Thus, inorganic acidic salts such as: Al(HSO4)3 17,18 Mg(HSO4)2 [19][20][21][22][23][24][25] and NaHSO4.H2O [23][24][25][26][27][28][29] could be recommended for above mentioned purposes. Although there are a few reports on the application of these salts in synthetic methodology, but only recently, more attention has been paid to the investigation of their potentials in organic synthesis.…”

“…Although there are a few reports on the application of these salts in synthetic methodology, but only recently, more attention has been paid to the investigation of their potentials in organic synthesis. [17][18][19][20][21][22][23][24][25][26][27][28][29] Now we wish to report a convenient method for deprotection of acetals or ketals using Al(HSO 4 ) 3 (I), Mg(HSO 4 ) 2 (II) and NaHSO 4 ·H 2 O (III) in the presence of wet SiO 2 (Scheme 1).…”

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

“…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.…”