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

Abstract

Synthesis of fused oxazolocoumarins has been achieved from the one‐pot tandem reactions of o‐hydroxynitrocoumarins with benzyl alcohol in toluene under catalysis in a sealed tube at 150°C. The catalysis was performed by gold nanoparticles supported on TiO2 (0.4 mol% Au) or FeCl3 (5%) or silver nanoparticles supported on TiO2 (1.7 mol% Ag).

One-pot Synthesis of 2-Substituted 4H-Chromeno[3,4-d]oxazol-4-ones from 4-Hydroxy-3-nitrocoumarin and Acids in the Presence of Triphenylphosphine and Phosphorus Pentoxide under Microwave Irradiation

“…Triphenylphosphine (PPh 3 ) is a versatile reagent for the reduction of a range of substrates including azides 32 (Staudinger reaction), disulfides, 33 sulfonyl chloride, 34 peroxides, 35 ozonides, 36 nitro compounds (for the Cadogan type reductive cyclization), 37 nitroso compounds, 38 and Noxides. 39 In a continuation of our studies on fused oxazolocoumarin derivatives, 1d, 30,31 we would like to present, herein, the use of PPh 3 for the one-pot synthesis of fused oxazolocoumarins from o-hydroxynitrocoumarin in the presence of acid and phosphorus pentoxide. The PPh 3 is utilized for the first time to our knowledge for the synthesis of oxazoles.…”

“…30 Very recently, we have synthesized oxazolocoumarins by one-pot tandem reactions of ohydroxynitrocoumarins with benzyl alcohol in toluene under catalysis with gold nanoparticles supported on TiO 2 , by FeCl 3 or by silver nanoparticles supported on TiO 2 . 31 Scheme 1 Reagents and conditions: (i) 2 (2 mL, 0.5 M), PPh 3 (3) (2.5 equiv), P 2 O 5 (4 equiv), MW irradiation, 130 °C or 140 °C, 1.5 h (not for 4a); (ii)2 (2 mL, 0.5 M), 5 mole % Pd/C (10%), H 2 1 atm, r.t., 1-3 h then P 2 O 5 (4 equiv), MW irradiation, 130 °C, 1 h; (iii) 2 (1.5 equiv), PPh 3 (3) (2.5 equiv), MW, 110-140 °C, 0.5-1 h; (iv) 2 (10 equiv), Pd/C 10% (0.05 equiv), H 2 1 atm, 110-140 °C, 12 h; (v) P 2 O 5 (6 equiv), toluene (10 mL), MW irradiation, 140 °C, 1 h.…”

4-Amino-2-(p-tolyl)-7H-chromeno[5,6-d]oxazol-7-one

“…The reaction of 4 with p-tolylmethanol (5) in a sealed tube in toluene in the presence of Au/TiO 2 (4 mol%) at 150 • C led to 4-nitro-2-(p-tolyl)-7H-chromeno [5,6-d]oxazol-7-one (6) (45% yield) accompanied by 4-amino-2-(p-tolyl)-7H-chromeno [5,6-d]oxazol-7-one (7) (13%). This reaction was performed in analogy to our recent work on the synthesis of fused oxazolocoumarins by the treatment of o-hydroxynitrocoumarins with benzyl alcohol catalyzed by Au/TiO 2 or Ag/TiO 2 or FeCl 3 [21]. During this process, a simultaneous reduction of nitro-to amine-group and oxidation of benzyl alcohol to benzaldehyde occurred, followed by imine formation from the amine and benzaldehyde, cyclization by addition of hydroxy-group to imine and oxidation of the intermediate oxazoline to oxazole.…”

“…Furthermore, substituted fused oxazolocoumarins were synthesized by the reduction of 4-hydroxy-3-nitrosocoumarin in acetic anhydride in the presence of Pd/C [19], or of 6-hydroxy-4-methyl-5-nitrocoumarin acetate in acetic acid with iron powder [20], or of 3-hydroxy-3-nitrocoumarins in liquid carboxylic acids in the presence of Pd/C or PPh 3 and P 2 O 5 [8]. Recently, we prepared oxazolocoumarins by one-pot tandem reactions of o-hydroxynitrocoumarins with benzyl alcohol in toluene under catalytical conditions using gold nanoparticles supported on TiO 2 , by FeCl 3 or by silver nanoparticles supported on TiO 2 [21].…”

One‐pot Synthesis of Fused Dipyranocoumarins from Dihydroxycoumarins and Propargyl Chlorides under Microwave Irradiation

“…The one‐pot synthesis reactions are considered as an efficient and greener procedure for the organic synthesis . In continuation of our investigations in the coumarin fields [2d, 3d, 11, 22, 23] and especially in the synthesis of fused pyranocoumarins and the use of MW irradiation and gold nanoparticles [22a, 23] in synthesis, we wish to present here the one‐pot synthesis of dipetalolactones from 5,7‐dihydroxycoumarins under MW irradiation, along with the synthesis of fused dipyranocoumarins from the intermediate dipropargyloxycoumarins using boron trifluoride etherate or gold nanoparticles under MWs. During the synthesis of 6,7‐dipropargyloxycoumarins isolated the interesting new exomethylene fused dioxino[2,3‐g]coumarins.…”