Amberlyst-15–Catalyzed Synthesis of 2-Substituted 1,3-Benzazoles in Water under Ultrasound

Abstract

A clean and general method has been developed for the synthesis of benzothiazole, benzoxazole, and benzimidazoles using Amberlyst-15 as a recyclable catalyst under ultrasound irradiation in water. The methodology is operationally simple, free from the use of hazardous organic solvents, and does not require the use of inert or anhydrous atmosphere. A number of 1,3-benzazole derivatives were prepared in good to excellent yields by using this methodology.

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GRAPHICAL ABSTRACT

Keywords:

• Amberlyst-15
• benzimidazole
• benzothiazole
• benzoxazole

ACKNOWLEDGMENT

The authors thank the management of Dr. Reddy's Institute of Life Sciences for continuous support and encouragement.

Notes

^a Reaction conditions: all the reactions were carried out using 2-aminophenol 1b (1.0 mmol), 4-chloro benzoic acid 2a (1.2 mmol), and Amberlyst-15 (10%, w/w) under ultrasoundirradiation in open air.

^b Isolated yield.

^c The reaction was carried out in the absence of Amberlyst-15 and ultrasound.

^d The reaction was carried out in the absence of Amberlyst-15.

^a Reaction conditions: 2-aminophenol 1b (1.0 mmol), 4-chlorobenzoic acid 2a (1.2 mmol), and Amberlyst-15 (10%, w/w) or recovered catalyst under ultrasoundirradiation in open air.

^a Reaction conditions: all the reactions were carried out using 1 (1.0 mmol), an appropriate acid 2 (1.0 mmol), and Amberlyst-15 (10%, w/w) in water at 90 °C under ultrasound irradiation in open air.

^b Isolated yield.

^a Reaction conditions: all the reactions were carried out using N-acyl derivative 6 (1.0 mmol) and Amberlyst-15 (10%, w/w) in water under ultrasound at 90 °C in open air.

^b Isolated yield.