Intramolecular Reductive Amidation of Unactivated Esters with Nitroarenes: A Telescoped Synthesis of Tetrahydropyrrolo/Pyrido[1,2-a]quinoxalinones

A reductive amidation of unactivated esters with nitroarenes, a key step in the telescopic synthesis of tetrahydropyrrolo[1,2-a]quinoxalinones and tetrahydropyrido[1,2-a]quinoxalinones, is reported. The process involves an intermolecular base-mediated SNAr reaction, followed by intramolecular reductive amidation employing sodium dithionite. The substrate scope coupled with the demonstration of the synthesis of pharmaceuticals is reported. The key features include nitro reduction at room temperature, easy purification without chromatography, amidation of unactivated esters without any externally added activating agent, and a telescopic process.

Dithionite-Mediated Tandem Nitro Reduction/Imine Formation/Intramolecular Cyclization for the Synthesis of Dihydro-benzothiadiazine-1,1-dioxides

A one-pot, tandem reductive annulation of 2-nitrobenzenesulfonamides with aldehydes to the synthesis of substituted 3,4-dihydro-2H-1,2,4-benzothiadiazine-1,1-dioxides in the presence of sodium dithionite (Na2S2O4) is reported under mild conditions. The method involves in situ reduction of the nitro group followed by condensation with aldehydes to form an imine, which upon subsequent intramolecular cyclization forms the product under one-pot conditions. The protocol features use of inexpensive Na2S2O4 as the exclusive reagent, appreciable functional group tolerance, broad substrate scope, high product yields, and scalability.

Multistep batch-flow hybrid synthesis of a terbinafine precursor

A three-step batch-flow hybrid process has been developed for an expeditious synthesis of the enynol key intermediate of antifungal terbinafine. This procedure involves consecutive organometallic steps without the necessity of any in-line purification: after a metalation by n-butyllithium, a selective addition of the lithium salt was elaborated followed by a Grignard reaction resulting in a high yield of 6,6-dimethylhept-1-en-4-yn-3-ol. Moreover, as an alternative to tetrahydrofuran, cyclopentyl methyl ether was used as solvent implementing a safe, sustainable, yet selective synthetic process. Even on a laboratory-scale, the optimized batch-flow hybrid process had a theoretical throughput of 41 g/h. Furthermore, the newly developed process provides an efficient synthesis route to the key-intermediate, while making acrolein obsolete, minimizing side-products, and enabling safe and convenient scale-up.

Application of reactor engineering concepts in continuous flow chemistry: a review

The adoption of flow technology for the manufacture of chemical entities, and in particular pharmaceuticals, has seen rapid growth over the past two decades with the technology now blurring the lines between chemistry and chemical engineering.

Improved batch and flow syntheses of the nonsteroidal anti-inflammatory COX-2 inhibitor celecoxib

The comparison of an improved conventional batch mode synthesis of the nonsteroidal anti-inflammatory COX-2 inhibitor celecoxib with its flow chemistry alternative is reported.

One-flow upscaling neutralization of an organophosphonate-derived pesticide/nerve agent simulant to value-added chemicals in a novel Teflon microreactor platform

Synthesizing value-added products from chemical warfare agents is a concept well beyond the usual notion of simply neutralizing the agents.

Integrating continuous flow synthesis with in-line analysis and data generation

Continuous flow synthesis of fine chemicals has successfully advanced from an academic niche area to a rapidly growing field of its own that directly impacts developments and applications in industrial settings. Whilst the numerous advantages of flow over batch processing are widely recognised and have led to a wider uptake of continuous flow synthesis within the community, we have reached a point where continuous flow synthesis has to transition from a stand-alone enabling technology to a readily integrated synthesis concept. Thus it is paramount to embrace a multitude of in-line analysis and purification techniques to not only allow for efficiently telescoped multi-step sequences but ultimately generate bioactivity data concomitantly on newly synthesised entities. This short review summarises the state of the art in this field and presents both challenges and opportunities that arise from this ambitious endeavour.

Landscape and opportunities for active pharmaceutical ingredient manufacturing in developing African economies

This review will highlight the opportunities that exist in the localization of cutting-edge manufacturing technologies within an African context.

Integrating reactive distillation with continuous flow processing

A continuous flow platform has been developed that integrates reactive distillation with modern flow reactor technology.

Continuous flow chemistry: where are we now? Recent applications, challenges and limitations

A general outlook of the changing face of chemical synthesis is provided in this article through recent applications of continuous flow processing in both industry and academia. The benefits, major challenges and limitations associated with the use of this mode of processing are also given due attention as an attempt to put into perspective the current position of continuous flow processing, either as an alternative or potential combinatory technology for batch processing.

Mild and selective reduction of aldehydes utilising sodium dithionite under flow conditions

We recently reported a novel hybrid batch–flow synthesis of the antipsychotic drug clozapine in which the reduction of a nitroaryl group is described under flow conditions using sodium dithionite. We now report the expansion of this method to include the reduction of aldehydes. The method developed affords yields which are comparable to those under batch conditions, has a reduced reaction time and improved space-time productivity. Furthermore, the approach allows the selective reduction of aldehydes in the presence of ketones and has been demonstrated as a continuous process.