Scale-Up of Microwave-Assisted Reactions in a Multimode Bench-Top Reactor

A green Heck reaction protocol towards trisubstituted alkenes, versatile pharmaceutical intermediates

The Heck reaction is widely employed to build a variety of biologically relevant scaffolds and has been successfully implemented in the production of active pharmaceutical ingredients (APIs). Typically, the reaction with terminal alkenes gives high yields and stereoselectivity toward the trans-substituted alkenes product, and many green variants of the original protocol have been developed for such substrates. However, these methodologies may not be applied with the same efficiency to reactions with challenging substrates, such as internal olefins, providing trisubstituted alkenes. In the present work, we have implemented a Heck reaction protocol under green conditions to access trisubstituted alkenes as final products or key intermediates of pharmaceutical interest. A set of preliminary experiments performed on a model reaction led to selecting a simple and green setup based on a design of experiments (DoE) study. In such a way, the best experimental conditions (catalyst loading, equivalents of alkene, base and tetraalkylammonium salt, composition, and amount of solvent) have been identified. Then, a second set of experiments were performed, bringing the reaction to completion and considering additional factors. The protocol thus defined involves using EtOH as the solvent, microwave (mw) irradiation to achieve short reaction times, and the supported catalyst Pd EnCat®40, which affords an easier recovery and reuse. These conditions were tested on different aryl bromides and internal olefines to evaluate the substrate scope. Furthermore, with the aim to limit as much as possible the production of waste, a simple isomerization procedure was developed to convert the isomeric byproducts into the desired conjugated E alkene, which is also the thermodynamically favoured product. The approach herein disclosed represents a green, efficient, and easy-to-use handle towards different trisubstituted alkenes via the Heck reaction.

Continuous Flow Synthesis of Heterocycles: A Recent Update on the Flow Synthesis of Indoles

Indole derivatives are among the most useful and interesting heterocycles employed in drug discovery and medicinal chemistry. In addition, flow chemistry and flow technology are changing the synthetic paradigm in the field of modern synthesis. In this review, the role of flow technology in the preparation of indole derivatives is showcased. Selected examples have been described with the aim to provide readers with an overview on the tactics and technologies used for targeting indole scaffolds.

My Twenty Years in Microwave Chemistry: From Kitchen Ovens to Microwaves that aren't Microwaves

This Personal Account describes the author's involvement in the field of microwave-assisted organic synthesis (MAOS) from the late 1990's starting out with kitchen microwave ovens right through to the development of a reactor in 2016 that - although not using microwave technology - in many ways mimics the performance of a modern laboratory microwave. The reader is taken along a journey that has spanned two decades of intense research on various aspects of microwave chemistry, and, at the same time, was intimately linked to key innovations regarding equipment design and development. A "behind the scenes" approach is taken in this article to share - from a very personal point of view - how specific projects and research ideas were conceived and developed in my research group, and how in general the field of microwave chemistry has progressed in the last two decades.

Practical and Scalable Organic Reactions with Flow Microwave Apparatus

Microwave irradiation has been used for accelerating organic reactions as a heating method and has been proven to be useful in laboratory scale organic synthesis. The major drawback of microwave chemistry is the difficulty in scaling up, mainly because of the low penetration depth of microwaves. The combination of microwave chemistry and flow chemistry is considered to overcome the problem in scaling up of microwave-assisted organic reactions, and some flow microwave systems have been developed in both academic and industrial communities. In this context, we have demonstrated the scale-up of fundamental organic reactions using a novel flow microwave system developed by the academic-industrial alliance between the University of Shizuoka, Advanced Industrial Science and Technology, and SAIDA FDS. In this Personal Account, we summarize the recent progress of our scalable microwave-assisted continuous synthesis using the SAIDA flow microwave apparatus.

Inverting the Selectivity of the Newman-Kwart Rearrangement via One Electron Oxidation at Room Temperature

The discovery that the Newman-Kwart rearrangement can be performed at room temperature by action of a simple and readily available oxidant, cerium ammonium nitrate, is described. The conditions give clean conversion when using electron-rich aromatic substrates, and the reactions are often quantitative. Computational studies support a reaction mechanism where the O-thiocarbamate is first oxidized to the radical cation, followed by nucleophilic attack by the ipso carbon of the aromatic system.

Synthesis, characterization and biological activities of 3-aryl-1,4-naphthoquinones – green palladium-catalysed Suzuki cross coupling

Antifungal and trypanocidal aryl-1,4-naphthoquinones were prepared through an aqueous Suzuki protocol with reflux or microwave irradiation.

Development of a highly efficient single-mode microwave applicator with a resonant cavity and its application to continuous flow syntheses

A new microwave applicator specifically designed for continuous flow synthesis has been developed and tested in the Fischer indole synthesis and in the Diels–Alder reaction to afford the reaction products at a scale of 100 g h⁻¹.

Synthesis of Polynitrostilbenes from 2,4,6-Trinitro-M-Xylene and 2,4,6-Trinitrotoluene by a Microwave-Assisted Solvent Free Method

A microwave-assisted method for the synthesis of polynitrostilbenes involving the condensation of 2,4,6-trinitro- m-xylene and 2,4,6-trinitrotoluene with aryl aldehydes in the presence of piperidine and silica-gel is reported. Compared with conventional methods, a shorter reaction time is required and this method has a lower environmental impact. A mechanism for the reaction is also proposed and supported by UV-Vis absorption spectroscopy.

On being green: can flow chemistry help?

The principles of Green Chemistry are important but challenging drivers for most modern synthesis programs. To meet these challenges new flow chemistry tools are proving to be very effective by providing improved heat/mass transfer opportunities, lower solvent usage, less waste generation, hazardous compound containment, and the possibility of a 24/7 working regime. This machine-assisted approach can be used to effect repetitive or routine scale-up steps or when combined with reagent and scavenger cartridges, to achieve multi-step synthesis of complex natural products and pharmaceutical agents.

Microwave-assisted synthesis of small molecules targeting the infectious diseases tuberculosis, HIV/AIDS, malaria and hepatitis C

The unique properties of microwave in situ heating offer unparalleled opportunities for medicinal chemists to speed up lead optimisation processes in early drug discovery. The technology is ideal for small-scale discovery chemistry because it allows full reaction control, short reaction times, high safety and rapid feedback. To illustrate these advantages, we herein describe applications and approaches in the synthesis of small molecules to combat four of the most prevalent infectious diseases; tuberculosis, HIV/AIDS, malaria and hepatitis C, using dedicated microwave instrumentation.