Spinning Reactors for Process Intensification of Flow Photochemistry.

The design of new and more sustainable synthetic protocols to access new materials or valuable compounds will have a high impact on the broader chemistry community. In this sense, continuous-flow photochemistry has emerged as a powerful technique which has been employed successfully in various areas such as biopharma, organic chemistry, as well as materials science. However, it is important to note that chemical processes must not only advance towards new or improved chemical transformations, but also implement new technologies that enable new process opportunities. For this reason, the design of novel photoreactors is key to advancing photochemical strategies. In this sense, the use of equipment and techniques embracing processes intensification is important in developing more sustainable protocols. Among the most recent applications, spinning continuous flow reactors, such as rotor reactors or vortex reactors, have shown promising performance as new synthetic tools. Nevertheless, there is currently no review in the literature that effectively summarizes and showcases the most recent applications of such type of photoreactors. Herein, we highlight fundamental aspects and applications of two categories of spinning reactors, the Spinning Disc Reactors (SDRs) and Thin Film Vortex reactors, critiquing the scope and limitations of these advanced processing technologies. Further, we take a view on the future of spinning reactors in flow as a synthetic toolbox to explore new photochemical transformations.

Mechanistic Insight into the Cu-Catalyzed C-S Cross-Coupling of Thioacetate with Aryl Halides: A Joint Experimental-Computational Study.

The mechanism of the Ullmann-type reaction between potassium thioacetate (KSAc) and iodobenzene (PhI) catalyzed by CuI associated with 1,10-phenanthroline (phen) as a ligand was explored experimentally and computationally. The study on C-S bond formation was investigated by UV-visible spectrophotometry, cyclic voltammetry, mass spectrometry, and products assessment from radical probes. The results indicate that under experimental conditions the catalytically active species is [Cu(phen)(SAc)] regardless of the copper source. An examination of the aryl halide activation mechanism using radical probes was undertaken. No evidence of the presence of radical species was found during the reaction process, which is consistent with an oxidative addition cross-coupling pathway. The different reaction pathways leading to the experimentally observed reaction products were studied by DFT calculation. The oxidative addition-reductive elimination mechanism via an unstable CuIII intermediate is energetically more feasible than other possible mechanisms such as single electron transfer, halogen atom transfer, and σ-bond methatesis.

Stereoselective one-pot synthesis of ß-alkylsulfide enol esters. Base-triggered rearrangement under mild conditions.

A stereoselective one-pot procedure was developed to prepare S-substituted (Z)-enol esters through a base-triggered rearrangement. This transition metal-free multicomponent approach can be performed under an air atmosphere at room temperature, tolerates a wide set of chemical functionalities and generally affords high isolated yields. The (Z)-selectivity arises from the [1,4]-S- to O-acyl migration.

Efficient Cu-catalyzed base-free C-S coupling under conventional and microwave heating. A simple access to S-heterocycles and sulfides.

S-aryl thioacetates can be prepared by reaction of inexpensive potassium thioacetate with both electron-rich and electron-poor aryl iodides under a base-free copper/ligand catalytic system. CuI as copper source affords S-aryl thioacetates in good to excellent yields, by using 1,10-phenanthroline as a ligand in toluene at 100 °C after 24 h. Under microwave irradiation the time was drastically reduced to 2 h. Both procedures are simple and involve a low-cost catalytic system. This methodology was also applied to the "one-pot" synthesis of target heterocycles, such as 3H-benzo[c][1,2]dithiol-3-one and 2-methylbenzothiazole, alkyl aryl sulfides, diaryl disulfides and asymmetric diaryl sulfides in good yields.