Abstract

Background: Now a days, organic synthesis in aqueous phase or including water and water/organic mixture as a solvent has been received great attention in the field of organic chemistry. As the microwave assisted organic synthesis (MAOS) is environmental friendly, inflammable, and allows simple separation and catalyst recycling. So, by the microwave assisted synthesis using water as a solvent, one can easily achieve the purpose of green chemistry. In view of the potential bioactivity of benzofuran and coumarin moieties, we have taken up the synthesis of some new furocoumarin-biaryl derivatives using Suzuki coupling by the combination of two prominent green chemistry principles, namely microwave assisted synthesis and aqueous phase reactions. We have taken up the synthesis by microwave as well as conventional methods.

Methods: The reaction of 8-acetyl-7-hydroxy-4-methyl Coumarin (1) with 2-bromo-1-(4-bromophenyl)ethanone (2) in presence of potassium carbonate, acetone yielded new furocoumarin, 4-(p-Bromobenzoyl)-3,10-dimethyl-5.13-dioxatricyclo[ 7.4.0.0^2,6]trideca-1(9),2(6),3,7,10-pentaen-12-one (3). Compound 3 on Suzuki coupling with different aryl boronic acids (4a-i) yielded the target molecules 4-[(4-Biphenylyl)carbonyl]-3,10-dimethyl-5.13-dioxatricyclo[7.4.0.0^2,6] trideca-1(9),2(6),3,7,10-pentaen-12-one analogues (5a-i)

Results: Compound 3 was characterized as 4-(p-Bromobenzoyl)-3,10-dimethyl-5.13-dioxatricyclo[7.4.0.02,6] trideca- 1(9),2(6),3,7,10-pentaen-12-one. In the IR spectrum of 3, a peak at 1078 cm-1 confirms the presence of C-O-C group. In ¹H NMR spectrum of 5a showed a singlet at δ 2.96 ppm corresponding to C₃-CH₃. In ¹³C NMR peak at δ 19.55 ppm, corresponding to methyl carbon attached to C₃, other peak at δ 184.2 ppm, corresponding to conjugated ketone functionality confirms the formation of furocoumarin skeleton. In the MS of 3 the base peak appeared at 397 corresponding to (M+H)⁺. Similarly, Compound 5a was characterized as 4-[(4-biphenylyl)carbonyl]-3,10-dimethyl-5.13- dioxatricyclo[7.4.0.0^2,6] trideca-1(9),2(6),3,7,10-pentaen-12-one. In the MS of 5a the appearance of base peak at 395 corresponding to (M+H)+ confirms the formation of Suzuki coupled product.

Conclusion: In conclusion, we have successfully synthesized a new series of 4-[(4-Biphenylyl)carbonyl]-3,10-dimethyl- 5.13-dioxatricyclo[7.4.0.0^2,6]trideca-1(9),2(6),3,7,10-pentaen-12-one derivatives (4.16a-i) under conventional and microwave irradiation methods using water as solvent. The microwave irradiation method was proved to be high yielding with higher rate of acceleration and eco-friendly.

Keywords: Aromatic boronic acid, antimicrobial activity, microwave irradiation, suzuki cross-coupling.

Graphical Abstract