Iron-Catalyzed 2-Arylbenzoxazole Formation from o-Nitrophenols and Benzylic Alcohols

Abstract

The iron-catalyzed 2-arylbenzoxazole formation from o-nitrophenols and benzylic alcohols using hydrogen transfer is described. Various 2-arylbenzoxazoles were selectively obtained in good to excellent yields. The reaction tolerated a wide range of functionalities. The alcohol oxidation, nitro reduction, condensation, and dehydrogenation were realized in a cascade without external reducing reagent and oxidant.

Transition‐Metal‐Catalyzed Hydrogen‐Transfer Annulations: Access to Heterocyclic Scaffolds

“…Based on these facts,r emarkable achievements have been made in this field of hydrogen-transfer annulations for the construction of heterocycles in the past few decades.T he notable developments in the catalytic systems have led to catalysts which are described as acceptorless,b ase-free, bifunctional, water-soluble,a nd recyclable,a nd makes this synthetic strategy an alternative for conventional synthetic transformations in academic and industrial settings.D espite several achievements in this area, there is still aneed for the development of efficient catalysts based on iron. Recently, af ew reports [44,45] were made on using iron as an efficient hydrogen-transfer catalyst, but it is still in its infancy.Indeed, this review describes what the current state-of-the-art is with regard to the hydrogen-transfer annulations.T here are still opportunities to design efficient, environmentally benign, and sustainable catalytic systems for the selective,atom-economic construction of complex heterocyclicf rameworks.…”

“…(29)]. [44] Inexpensive and efficient catalytic methods for the preparation of benzoxazoles and benzothiazoles from alcohols and 2-aminophenols and thiophenols,r espectively,w ere developed using iron(II) phthalocyanine (FePc) as the catalyst [Eq. (30)].…”

Magnetic Co‐doped NiFe2O4 Nanocomposite: A Heterogeneous and Recyclable Catalyst for the One‐Pot Synthesis of Benzimidazoles, Benzoxazoles and Benzothiazoles under Solvent‐Free Conditions

“…The stirring of the solution was continued for 1 h. After completion of the reaction, the product was washed three times with distilled water and once with absolute ethanol, and finally annealed in oven at 80 C for 3 h and then calcined at 300 C for 2 h to form the Ni 0.6 Co 0.4 Fe 2 O 4 nanocatalyst. 31 4 8 1 Co(OH) 2 /CoO(II)(10 mol%)/ Ethanol, air, rt 22 6/4 93/96 AlKIT-5/CH 3 CN, reflux 54 4 9 5 Ionic liquid, 90 C 55 13 min 89 Cu(OH) 2 / CH 3 OH, rt 56 4 9 8 Triphenylphosphine/trichloroisocyanuric acid, 1, 4-dioxane, reflux 57 1 9 0 T3P (in AcOEt), DIPEA/MW, 160 C 58 30 min 77 FHS/ EtOH, rt 29 25 min 95 HMTA-Bromine(10 mol%)/ MeCN, rt or MW 44 59 44 min 83 MCM-41-SO 3 H/ H 2 O, rt 60 10 min 90 Present work 2 97 NiEuFe 2 O 4 /water, reflux 24 50 min 86 Fe/150 C, argon 61 12 85 DCM, NEt 3 / MW, 40 C 62 2 8 2 PIFA/ EtOH, MW, 80 C 63 15 min 87 Triphenylphosphine/trichloroisocyanuric acid, 1, 4-dioxane, reflux 57 4 9 7 Glycerol:H 2 O/ 90 C 40 4 9 0 CeCl 3 (15 mol%), NaI (10 mol%), toluene/O 2 , 100 C 43 36 73 Present work 15 min 98 VOSO 4 /EtOH, rt 64 45 min 92 T 3 P (in AcOEt), DIPEA/MW, 100 C 58 10 min 91 PIFA/ EtOH, MW, 80 C 63 15 min 87 Triphenylphosphine/trichloroisocyanuric acid, 1, 4-dioxane, reflux 57 5 min 90 FHS/EtOH, reflux 29 20 min 91 HMTA-bromine(10 mol%) MeCN, rt or MW 44 6 8 5 FeCl 3 /montmorillonite K-10, air, CH 3 OH 41 1 8 5 General procedure for the preparation of benzimidazoles, benzoxazoles, and benzthiazoles A mixture of o-phenylenediamines, o-aminothiophenol, or o-aminophenol (1 mmol), benzaldehyde derivatives (1.2 mmol), and Co-doped NiFe 2 O 4 nanoparticles (10% mol, 0.023 g) was stirred at 70 C. The progress of the reaction was monitored by thinlayer chromatography; TLC, hexane/ethyl acetate, 10:2. After completion of the reaction, hot ethyl acetate (5 mL) was added to the mixture, and the nanomagnetic catalyst was separated from the reaction mixture using an external magnet.…”

Synthesis of Fused Oxazolocoumarins from o‐Hydroxynitrocoumarins and Benzyl Alcohol Under Gold Nanoparticles or FeCl3 Catalysis

“…Very recently the Ag/TiO 2 NPs were applied for an analogous synthesis from aldehydes and carboxylic acids derivatives in water. Recently 2‐arylbenzoxazoles were synthesized in a one‐pot tandem procedure from o ‐nitrophenols and benzyl alcohols under dppf catalysis or catalysis by gold NPs supported on titanium oxide .…”