**4. Conclusions**

We have proposed here a synthetic and computational study of halodediazotation reactions (a Sandmeyer's class of reactions) carried out in deep eutectic solvent-like mixtures. The computational results are coherent with the experimental findings; the reactions of the control electron-poor **1a** are faster than that of the control electron-rich **1f**, and the halogenations are always much faster than the solvolysis that would yield the mixed ethers **6a** and **6f**. Both halogenations and the solvolysis take place through a mechanism similar to that of front-SN2. Diazonium salts are resourceful building blocks in organic synthesis, and the last few years have seen a dramatic resurgence of their chemistry, as new functionalities have been introduced on their aromatic ring. The marriage between diazonium salts and deep eutectic solvents, which have also been defined as "the solvents of the century" [5], can become not only a valid tool to make their chemistry more sustainable but can also allow the exploration of new types of hitherto unknown reactivity.

**Supplementary Materials:** The following supporting information can be downloaded at: https:// www.mdpi.com/article/10.3390/molecules27061909/s1, Computational method, Tables of calculated absolute and relative energies, Pictures and Cartesian Coordinates of all optimized structures, IRCs from the TSs for the chlorination and solvolysis of **1a'**, physical and NMR data of aryl halides **2, 4, 5** and NMR of glycerol/KBr solvent system can be downloaded at: https://www.mdpi.com/article/ 10.3390/molecules27061909/s1. References [58–82] are cited in the supplementary materials.

**Author Contributions:** G.G.: general organization, DFT calculations; M.B.: general organization, analysis of solvent systems; A.A.: halodediazotation reactions; C.R.: halodediazotation reactions; S.D.: general organization, halodediazotation reactions. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Data Availability Statement:** The data reported in this article can be obtained from the authors upon reasonable request.

**Acknowledgments:** This work was Presented at VI International Symposium «The Chemistry of Diazo Compounds and Related Systems» Saint Petersburg, Russia, 6-10/9/2021. Dughera, S.; Ghigo, G.; Bonomo, M.; Antenucci, A.; Barolo, C.; Gontrani, L.; Reviglio, C. How do diazonium salts behave in Deep Eutectic solvents? VI International Symposium "The Chemistry of Diazo Compounds and Related Systems"-Book of Abstracts. P. 41 (ISBN 978-5-9651-1365-1).

**Conflicts of Interest:** The authors declare no conflict of interest.

**Sample Availability:** Samples of the compounds **2**, **4**, **5** are available from the authors.
