:
Thiamine hydrochloride is reported to be highly competent promoter for the synthesis of bis(indolyl)methanes
under solvent free conditions using microwave irradiation and ultrasonicator heating in aqueous media. Vitamin B1 is an
economical, non-toxic, nonflammable and water soluble green organocatalyst. Moreover, the simple approach, easily operational, short reaction time, high yield and using a little quantity of thiamine hydrochloride makes this method an alternative
approach. Present protocol is a simple and eco-friendly approach for the synthesis of bis(indolyl)methanes under microwave
and ultrasonicator condition.
Background:
Multicomponent reactions involve the simultaneous reaction of three or
more components which deliver the product that incorporates the elements of all starting materials. A
combination of multicomponent reaction and green solvents like water and the use of nonconventional
energy sources like microwave or ultrasonication are important features of ideal green synthesis.
Therefore, the design of a new multicomponent reaction and improvement of an already known
multicomponent reaction with a green procedure has attracted the attention of the scientific community.
Isoxazole derivatives are well known for their biological activities such as antifungal, analgesic,
antitumor, antioxidant, antimicrobial, COX-2 inhibitory, anti-inflammatory, antiviral, and antimycobacterial.
Objective:
To develop a green methodology for the synthesis of 4H-isoxazol-5-ones derivatives.
Results:
Itaconic acid was used as a green catalyst for the synthesis of 4H-isoxazol-5-ones derivatives
under conventional as well as ultrasound irradiation technique. Ultrasound irradiation condition requires
less time for the completion of the reaction and also the yields were better.
Methods:
We have reported Itaconic acid as a green homogenous organocatalyst under ultrasound
irradiation for the synthesis of 4H-isoxazol-5-ones derivatives.
Conclusion:
In conclusion, we have developed a green methodology for the synthesis of 4Hisoxazol-
5-ones derivatives. Itaconic acid is used as an organocatalyst which is biodegradable and
nonhazardous. Water is used as a green solvent. Ultrasonication is used as a non-conventional green
energy source. Ambient reaction conditions are used to carry out transformation for multicomponent
reaction. Metal-free, mineral acid-free synthesis are key features of the present protocol.
Aim and Objective: To explore the use of naturally occurring biodegradable organic acids as a catalyst
in organic synthesis. The development of a simple, inexpensive, highly efficient yet ecofriendly catalyst
for the synthesis of bis(indolyl)methanes is explored.
Materials and Method:
A mixture of indole 1a (1.0 g, 8.53 mmol), benzaldehyde 2a (0.45 g. 4.26 mmol), and
itaconic acid (0.12 g, 0.92 mmol, 20 mol%), in H2O (5.0 mL) was refluxed at 100°C for indicated time. After
the completion of the reaction (TLC check), the reaction mixture was cooled to room temperature and extracted
with ethyl acetate (3 × 5.0 mL), organic layer was dried over Na2SO4 and concentrated under vacuum. The
crude residue was purified by column chromatography on silica gel using ethyl acetate:hexane as an eluent.
Results:
Initially optimal reaction conditions were developed for the synthesis of bis(indolyl)methanes by selecting
model reaction between indole and benzaldehyde. It was found that optimal conditions for the synthesis
of bis(indolyl)methanes are use of indole (1.0 mmol), aldehyde (0.5 mmol) and catalyst 20 mol% in water as a
solvent, under air atmosphere and at 100°C. Moreover, it was found that aqueous solution of the catalyst can be
reused with the same catalytic efficiency for ten times without any pre-treatment. This is an important achievement
with regard to the efficiency and reusability of the catalyst in synthesis.
Conclusion:
We have shown that itaconic acid in water can be used as an excellent green catalyst with high
reusability. It efficiently catalyzes electrophillic substitution reaction of indoles (ESRI) with various aldehydes
to give the corresponding BIMs in an efficient manner. Therefore, itaconic acid in water as a catalyst can be a
good alternative for the use of hazardous mineral acid and Lewis acid catalyst.
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