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 to 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 was added to the first pot. After
completion of 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 compounds
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 agree with some principles of green chemistry.