Title:L-Ascorbic Acid: A Green and Competent Promoter for Solvent-Free Synthesis of Flavones and Coumarins under Conventional as well as Microwave Heating
Volume: 13
Issue: 10
Author(s): Rohit Arvind Dengale, Nitin Madhu Thorat and Shankar Ramchandra Thopate
Affiliation:
Keywords:
L-Ascorbic acid, benzopyrone, flavone, coumarin, solvent-free synthesis, promoter.
Abstract: Background: An expeditious approach has been developed for the synthesis of two distinct
classes of benzopyrones viz. flavones and coumarins under solvent-free conditions. L-Ascorbic acid was
found to be an effective promoter under microwave irradiation and conventional heating. Various
benzo-α-pyrones and benzo-γ-pyrones were synthesized with overall good yields. The present protocol
is highly facile and needs no column chromatography for purification and therefore it would serve as an
effective and compatible method under both microwave irradiation and conventional heating.
Results: The catalytic ability of L-ascorbic acid was investigated for the synthesis of flavones and coumarins.
For this purpose, cyclodehydration of 1-(2-hydroxyphenyl)-3-aryl-1,3-propanedione and Pechmann
coumarin synthesis, reactions were selected. And accordingly, it was observed that one mole of
L-ascorbic acid was necessary for the completion of reaction. In all the cases, the desired flavones were
smoothly generated with good to excellent yields; indicating its excellent tolerance for various functional
groups. However, electron donating groups favors coumarin synthesis under these conditions. All
the reaction mixtures were carefully analyzed and NMR indicates high conversions and lack of side
products.
Conclusion: We have developed L-ascorbic acid-promoted, solvent-free and simple method for the synthesis
of benzo-α-pyrones and benzo-γ-pyrone under microwave irradiation as well as conventional
heating in good to excellent yields. The notable advantages of this method are solvent-free conditions,
inexpensive and efficient eco-friendly promoter, and shorter reaction time and can be carried out under
air. This methodology is highly facile and requires no column chromatography for purification. The resulting
flavones and coumarins are versatile building blocks in the construction of heterocyclic architectures,
dominant in natural products. Further studies of exploiting the efficiency of L-ascorbic acid as a
promoter in synthesis of various heterocyclic compounds are in progress.
