Abstract
AbstractEnvironmentally benign and biodegradable lactic acid is identified as alternative solvent and catalyst for the tandem one-pot synthesis of Hantzsch 2-aminothiazole derivatives (4) from readily available aralkyl ketones (1) through in situ regioselective α-bromination using N-bromosuccinimide (2) followed by heterocyclization using thiourea (3) at 90–100°C. The major advantages of the present method include short reaction times (10–15 min), practical, simple to perform, easy work-up, good yield of products (up to 96%), productive for large-scale applications, free from apply of α-bromoketones (lachrymator) as substrates, avoids column purification. Hence, the present method meets with the concepts of both Wender’s “ideal synthesis” and sustainable chemical process.
Highlights
The growing interest in developing simple, more convenient methods for the synthesis of medicinally important thiazole moiety has great demand both in academic, chemical, and pharmaceutical domains (Dondoni, 1985)
It is concluded that the present method is an attractive addition to the sustainable chemical processes
We report a simple, more convenient, practical method in which lactic acid acts as green catalyst and solvent for the one-pot synthesis of Hantzsch 2-aminothiazole derivatives (4) within 10–15 min from readily available aralkyl ketones (1) through in situ regioselective α-bromination using N-bromosuccinimide (2) followed by heterocyclization using thiourea (3) at 90–100°C (Scheme 1)
Summary
The growing interest in developing simple, more convenient methods for the synthesis of medicinally important thiazole moiety has great demand both in academic, chemical, and pharmaceutical domains (Dondoni, 1985). Extensive use of conventional solvents and hazardous catalysts became mandatory for their preparation which is leading to environmental pollution These are mostly prepared from α-bromoketones that are difficult to store and not accessible. The growing interest in developing simple, safe, more convenient, and sustainable scale-up methods for the synthesis of these thiazole synthetic precursors from readily available ketones has great demand in academic, chemical, and pharmaceutical domains. The Hantzsch thiazole synthesis (Hantzsch & Weber, 1887) is a powerful synthetic tool for the construction of the five-membered 2-aminothiazole derivatives Even though it was introduced more than one century ago, still the development of new Hantzsch-based methods is warranted. Most of the reported methods suffer from one or more disadvantages including use of hazardous and toxic reagents, long reaction times, low selectivity of the products, use of toxic and volatile solvents as well as catalysts, environmentally hazardous processes, low yields and difficulties in work-up and isolation of products and oppressive operational procedures
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