US 11,987,585 B2
Process for preparing substituted imidazo[4,5-c]pyrazoles
Abir Said Ibrahim Abdel-Naby, Dammam (SA); and Sara Nabil, Dammam (SA)
Assigned to Imam Abdulrahman Bin Faisal University, Dammam (SA)
Filed by Imam Abdulrahman Bin Faisal University, Dammam (SA)
Filed on Feb. 9, 2023, as Appl. No. 18/166,898.
Application 18/166,898 is a division of application No. 17/462,944, filed on Aug. 31, 2021, abandoned.
Prior Publication US 2023/0183254 A1, Jun. 15, 2023
Int. Cl. C07D 487/04 (2006.01); B01J 21/04 (2006.01); B82Y 30/00 (2011.01)
CPC C07D 487/04 (2013.01) [B01J 21/04 (2013.01); B82Y 30/00 (2013.01)] 7 Claims
 
1. A process for preparing a compound of Formula (I):

OG Complex Work Unit Chemistry
wherein:
R1 is H, halogen, alkyl, cycloalkyl, aryl, or heteroaryl;
R2 is H, halogen, alkyl, cycloalkyl, aryl, or heteroaryl;
R3 is H or C1-C3 alkyl; and
R4 is H, alkyl, cycloalkyl, aryl, or heteroaryl;
with the proviso that R2 is not pyrimidinyl or triazinyl;
wherein the process comprises the following steps:
(1) dissolving chitosan in acetic acid to obtain a chitosan solution;
(2) adjusting the pH of the chitosan solution formed in step (1) above to a pH in the range of 6 to 7;
(3) adding an aqueous suspension of aluminum oxide nanoparticles portion-wise to the chitosan solution formed in step (2) above, followed by stirring to form an aqueous mixture containing the chitosan solution and aluminum oxide nanoparticles;
(4) solution casting the aqueous mixture containing chitosan and aluminum oxide nanoparticles formed in step (3) above onto a carrier substrate, followed by drying to form a chitosan-alumina nanocomposite film, wherein the chitosan-alumina nanocomposite film is a heterogeneous base catalyst;
(5) reacting a compound of Formula (III):

OG Complex Work Unit Chemistry
wherein:
R1 is H, halogen, alkyl, cycloalkyl, aryl, or heteroaryl;
R2 is H, halogen, alkyl, cycloalkyl, aryl, or heteroaryl; and
R3 is H or C1-C3 alkyl;
with the proviso that R2 is not pyrimidinyl or triazinyl;
with a compound of Formula (IV):

OG Complex Work Unit Chemistry
wherein:
R4 is H, alkyl, cycloalkyl, aryl, or heteroaryl;
in the presence of ethanol and the chitosan-alumina nanocomposite film formed in step (4) above [10-20 wt % based on the weight of the compound of Formula (III)], to form a reaction mixture comprising ethanol and the heterogeneous base chitosan-alumina nanocomposite film catalyst;
(6) filtering the reaction mixture formed in step (5) above to remove the heterogeneous base chitosan-alumina nanocomposite film catalyst, followed by collecting a filtrate containing ethanol;
(7) evaporating ethanol from the filtrate collected in step (6) above, to precipitate the crude compound of Formula (I) above; and
(8) recrystallizing the crude compound of Formula (I) precipitated in step (7) above from ethanol, to form the compound of Formula (I):

OG Complex Work Unit Chemistry
wherein:
R1 is H, halogen, alkyl, cycloalkyl, aryl, or heteroaryl;
R2 is H, halogen, alkyl, cycloalkyl, aryl, or heteroaryl;
R3 is H or C1-C3 alkyl; and
R4 is H, alkyl, cycloalkyl, aryl, or heteroaryl;
with the proviso that R2 is not pyrimidinyl or triazinyl.