Review articleFlow chemistry: A green opportunity for organochalcogen chemistry
Introduction
In the last years flow chemistry emerged as a valuable tool for the continuous synthesis of fine chemicals, and, as a result it attracted remarkable attention and several reviews and book chapters have been dedicated to the topic [1]. Noteworthy, from a green chemistry perspective, flow technologies offer several advantages over batch processes [2,3] such as the possibility to efficiently control reaction conditions [1] granting a rapid scalability and an easier transition from lab-scale to an industrial-scale preparation of compounds [4, 5, 6]. A comprehensive dissertation of the pros and cons of flow technologies is out of the scope of the present review which aims to highlight the most recent examples in the field of organochalcogens chemistry with particular emphasis on the preparation of sulfur and selenium-containing compounds published in the last years. This is meant to update the sole book chapter [7] ever published in this specific topic stressing that, to the best of our knowledge, no review article has been never published.
The manuscript is structured in two main parts, one dealing with the chemistry of organosulfur compounds and a smaller one, dealing with the few examples of organoselenium chemistry reported in the timeframe we have chosen to cover.
Section snippets
Preparation of sulfur containing heterocycles
Aleman and coworkers in 2020 reported the preparation of isothiazoles by the powerful merging of continuous synthesis and photochemistry [8]. Authors used as starting compounds α-iminooxy acids 1 that, in the presence of 9-mesityl-10-methylacridinium perchlorate as photocatalyst and visible light irradiation, gives a radical that fragmentates with loss of CO2 and acetone followed by cyclization that delivers isothiazole 2 (Figure 1, a). The transition from batch to flow conditions needed the
Selenium
Even if in the last two decades organoselenium chemistry is rising due to the possibility to synthesize compounds endowed with remarkable biological activities [37, 38, 39] and valuable green reagents exploitable in a wide array of chemical transformations [40, 41, 42], there are a few examples of continuous approaches and almost all are very recent.
A biomimetic catalytic approach was developed by us for the conversion of sulfides into the corresponding sulfoxides and sulfones (Figure 4, a). In
Summary
In conclusion, the literature analysis revealed that flow chemistry is a valuable option to perform transformation in the field of organosulfur chemistry. In case of organoselenium chemistry, there is room for further investigation due to the low number of examples reported to date. Noteworthy, flow processes proved to be highly orthogonal with other enabling approaches such as photo and electrochemistry, and the present review tries to deliver the message that this is valid also for
Declaration of competing interest
The authors declare the following financial interests/personal relationships that may be considered as potential competing interests:
Luca Sancineto reports administrative support was provided by University of Perugia Department of Pharmaceutical Sciences.
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