Koleda, O.; Prenzel, T,; Winter, J.; Hirohata, T.; Gálvez-Vázquez, J.; Schollmeyer, D.; Inagi, S.; Suna, E.; Waldvogel, S. R.; Chem. Sci. 2023, 14, 2669-2675. DOI: 10.1039/D3SC00266G
Abstract
Cathodic synthesis provides sustainable access to 1-hydroxy- and 1-oxy-quinazolin-4-ones from easily accessible nitro starting materials. Mild reaction conditions, inexpensive and reusable carbon-based electrode materials, an undivided electrochemical setup, and constant current conditions characterise this method. Sulphuric acid is used as a simple supporting electrolyte as well as a catalyst for cyclisation. The broad applicability of this protocol is demonstrated in 27 differently substituted derivatives in high yields of up to 92%. Moreover, mechanistic studies based on cyclic voltammetry measurements highlight a selective reduction of the nitro substrate to hydroxylamine as a key step. The relevance for preparative applications is demonstrated by a 100-fold scale-up for gram-scale electrolysis.