PHOTOFLOW SUBSTITUTE UPDATE

The second section investigates progress on continuous photochemical approaches targeting greener and more sustainable synthesis means. To accomplish this, we first review the design of various reactor types and outline innovative aspects that aid in overcoming traditional bottlenecks. In addition, we wished to evaluate whether there had been significant uptake of this technology by chemists outside traditional academic laboratories and whether flow photochemistry had advanced to be a viable option to generating bioactive molecules in industrial settings. This appears both timely and paramount, as the last ten years have provided the foundations to now apply continuous photochemistry to the syntheses of various biologically active entities-drugs, natural products and their precursors. As the field of continuous flow photosynthesis is moving forward at fast pace, we wish to provide a focused review on its impact on generating bioactive molecules. Finally, continuous flow processing allows for simple reaction scale-up of the resulting photoreaction without alteration of reaction parameters and the short residence times within the photoreactor reduce the likelihood of decomposition of substrate or product due to over-radiation.Īs a consequence of the successful union of flow reactor technology with modern photochemical applications, a growing body of literature has emerged, including topical reviews by leading experts in the field. Oftentimes low-energy, tunable light sources are favored in combination with suitable cooling mechanisms to effectively control both temperature and energy input. Furthermore, by placing the light source near the reactor coil or microchip of the flow set-up, very efficient and uniform radiation of the substrate can be achieved. As such, the short path lengths provided by narrow, light-permeable tubing ensure that light can easily penetrate the substrate solution, thereby mitigating limitations commonly arising from the Beer–Lambert law.

In addition, continuous flow technology has had a major impact on popularizing photochemical reactions, as it not only provides the tools to effectively perform photochemical reactions, but moreover helps overcoming limitations that are inherent to photochemistry. Consequently, a plethora of known and newly developed photoreactions has been reported in the literature, rendering facile access to diverse chemical entities through selective transformations that oftentimes offer orthogonal approaches to the synthetic chemist. The availability of suitable light sources, ranging from light-emitting diodes (LED) to continuous fluorescent lamps (CFL) and powerful UV lamps (e.g., medium-pressure mercury lamp), furthermore, has driven this development. This renewed interest in utilizing light to bring about chemical reactions is largely fueled by a desire to realize more sustainable approaches for target molecule synthesis, along with significant advances in the field of photoredox catalysis where both transition metals and organic dyes have been exploited.

The last decade has witnessed a much-welcomed renaissance and subsequent exploitation of photochemical transformations within the chemistry community.

PHOTOFLOW SUBSTITUTE UPDATE

It is hoped that this report provides a valuable update on this important field of synthetic chemistry which may fuel developments in the future. A final section outlines remaining challenges and areas that will benefit from further developments in this fast-moving area. Dedicated sections present the variety of suitable reactor designs and set-ups available a short discussion on the relevance of greener and more sustainable approaches and selected key applications in the area of bioactive structures.

To this end we highlight key developments in this field that have contributed to the progress achieved to date. In this focused review article, we wish to evaluate the standing of the field of continuous flow photochemistry with a specific emphasis on the generation of bioactive entities, including natural products, drugs and their precursors. Additionally, the availability of modern continuous flow reactors has enabled widespread applications in view of more streamlined and custom designed flow processes. The last decade has witnessed a remarkable development towards improved and new photochemical transformations in response to greener and more sustainable chemical synthesis needs.

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