Abstract
An efficient continuous flow process is reported for the synthesis of various 1,3,4-oxadiazoles via an iodine-mediated oxidative cyclisation approach. This entails the use of a heated packed-bed reactor filled with solid K2CO3 as a base. Using DMSO as solvent, this flow method generates the target heterocycles within short residence times of 10 minutes and in yields up to 93%. Scale-up of this flow process was achieved (34 mmol/h) and featured an integrated quenching and extraction step. Lastly, the use of an automated in-line chromatography system was exploited to realise a powerful flow platform for the generation of the heterocyclic targets.
Highlights
As a potential application of our previously reported synthesis of useful bicyclo[1.1.1]pentane (BCP) building blocks [36], we investigated their use in the oxadiazole-forming reaction
The incorporation of an in-line extraction reduced the risk of contact with toxic and corrosive iodine in addition to eliminating a tedious unit operation
The reaction was demonstrated to be readily scalable with a productivity of 34 mmol/h being achieved for oxadiazole 2j
Summary
The application of enabling technologies in chemistry has received a surge in interest in recent years [1-4]. At the forefront of this revolution has been the advent of flow chemistry and its increasing utility in synthetic chemistry [5-8]. Carrying out a reaction in continuous flow mode can improve its efficiency in several ways, including decreasing reaction times, increasing yields, or eliminating tedious unit operations by incorporating them in-line in a telescoped manner. These improvements are typically not limited to the chemistry itself but can result in the generation of less waste, reducing the harmful environmental impact of various processes [12-15]. This has led to a significant development in continuous flow platforms, in industry [1620]
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