Abstract
Polyhydroquinoline derivatives have been efficiently prepared on polyethylene glycol (PEG) via one-pot condensation of PEG-bound acetoacetate, 1,3-cyclohexanedione, ammonium acetate and the appropriate aromatic aldehyde in the presence of catalytic amounts of polyphosphoric acid by solvent-free microwave irradiation. The procedure provided the target compounds in excellent yield and purity with a facile work-up procedure.
Highlights
4-Substituted 1,4-dihydropyridines (1,4-DHPs) are analogues of NADH coenzymes and an important class of drugs.[1]
As part of an ongoing research program focused on the use of polyethylene glycol (PEG)-supported β-keto ester in liquid-phase organic synthesis,[14] we developed the Hantzsch reaction on PEG that offers the desired products, i.e. polyhydroquinoline derivatives, in excellent yield and high purity after the direct cleavage from PEG, maintaining the simplicity of the one-pot procedure (Scheme 1)
The conversion of the terminal hydroxyl groups on PEG to 1 was indicated by C=O absorptions at 1743 and 1718 cm-1 in the IR spectrum, corresponding to ester and ketone carbonyl groups, respectively, and was determined by 1H NMR to be quantitative. In this liquid-phase synthetic process, the condensation of PEG-bound acetoacetate 1 with 1,3-cyclohexanedione (2), aromatic aldehydes and ammonium acetate would be the key step for the success of this protocol
Summary
4-Substituted 1,4-dihydropyridines (1,4-DHPs) are analogues of NADH coenzymes and an important class of drugs.[1]. 2 hydrogenation methods for the conversion of these compounds to pyridines have been investigated intensively.[3] Classical methods for the synthesis of 1,4-dihydropyridines are one-pot condensation of an aldehyde with ethyl acetoacetate and ammonium acetate, either in acetic acid or under reflux in alcohols.[4] these methods suffer from several drawbacks such as a long reaction times, an excess of organic solvent, lower product yields, and harsh refluxing conditions.
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