Aims & Objective:
An efficient procedure for the synthesis of pyrido[2,1-a]isoquinoline derivatives in excellent yields
was investigated using catalyst-free multicomponent reaction of phthaladehyde, methylamine, activated acetylenic compounds,
alkyl bromides and triphenylphosphine in water under ultrasonic irradiation at room temperature. In addition, Diels-Alder
reactions of pyrido[2,1-a]isoquinoline derivatives with activated acetylenic compounds under ultrasonic irradiation are
investigated in two procedures. The advantages of this procedure compared to report methods are short time of reaction, high
yields of product, easy separation of product, clean mixture of reaction and green media for performing reaction. In addition,
because of having isoquinoline core in synthesized compounds, in this research antioxidant activity of some synthesized
compounds was studied.
Materials and Methods:
To a stirred mixture of phthalaldehyde 1 (2 mmol) and methylamine 2 (2 mmol) in water (3 mL) under
ultrasonic irradiation was added activated acetylenic compounds 4 after 20 min. Alkyl bromide 3 and triphenylphosphine 5 react in
another pot in water (3 mL) under ultrasonic irradiation for 15 min. After this time, this mixture added to first pot. After completion
the reaction, the solid residue was separated by filtration and washed with Et2O to afforded pure title compound 6.
Results:
In this work, generation of pyrido[2,1-a]isoquinoline derivatives 6 are performed using phthalaldehyde 1, methylamine
2, α-halo substituted carbonyls 3, activated acetylenic comompouds 4 and triphenylphosphine 5 in water under ultrasonic
irradiation condition at room temperature in excellent yield at short time.
Conclusion:
In summary, multicomponent reaction of phthaladehyde, methylamine, activated acetylenic compounds, alkyl
bromides and triphenylphosphine in water under ultrasonic irradiation at room temperature produced pyrido[2,1-a]isoquinoline
derivatives in excellent yields. Also, Diels-Alder reaction of pyrido[2,1-a]isoquinoline derivatives with activated acetylenic
compounds and triphenylphosphine under ultrasonic irradiation is investigated in two procedures. Also, the antioxidant activities
of 6a, 6c, 6g and 6i were evaluated by DPPH radical scavenging and ferric reducing power analyzes. The compounds 6a exhibit
excellent DPPH radical scavenging activity and FRAP compared to synthetic antioxidants BHT and TBHQ. The chief benefits
of our method are high atom economy, green reaction conditions, higher yield, shorter reaction times, and easy work-up, which
are in good agreement with some principles of green chemistry.
Hetero-Diels–Alder reactions of hetaryl and aryl thioketones with acetylenic dienophiles
