Complementary Reactivity in Selective Radical Processes: Electrochemistry of Oxadiazolines to Quinazolinones

Abstract

Electrochemistry has recently emerged as a sustainable approach for efficiently generating radical intermediates utilizing eco-friendly electric energy. An electrochemical process was developed to transform 1,2,4-oxadiazolines under mild conditions. The electrochemical N−O bond cleavage at a controlled oxidation potential led to the selective synthesis of quinazolinone derivatives that could not be obtained by photocatalytic radical processes, indicating complementary reactivities in radical processes. The electrochemical reaction pathways were fully revealed by density functional theory-based investigations.

N–O Bond Activation by Energy Transfer Photocatalysis

“…Besides the above-mentioned spiro-azalactam, benzimidazole, and sulfoximine products, quinazolinones were generated selectively from 1,2,4-oxadiazolines by electrochemistry through heterolytic N–O bond cleavage at a controlled oxidation potential, indicating complementary reactivities in radical processes (Scheme ). Notably, an identical reaction profile to give quinazolinones in the presence of oxygen under thermal conditions was reported by the Chiba group …”

“…Based on the redox potentials of reactivities in radical processes (Scheme 3). 66 Notably, an identical reaction profile to give quinazolinones in the presence of oxygen under thermal conditions was reported by the Chiba group. 67…”

Visible‐Light Induced C(sp2)−H Amidation with an Aryl–Alkyl σ‐Bond Relocation via Redox‐Neutral Radical–Polar Crossover

“…[23] It should be mentioned that Cho recently showed that iminyl radicals can induce similar transformations albeit with unsatisfactory regioselectivity. [24] To interrogate two regulatory pathways in the formation of skeletally rearranged lactam isomers, we conducted density functional theory (DFT) calculations (Figure 1 b-d). Reductive SET of 3 a leads to a smooth NÀO bond cleavage with 13.0 kcal mol À1 barrier (see the Supporting Information for details).…”

“…The lactam formation was also found to be efficient even with substrates containing additional groups at the b-position relative to the carbonyl group. For instance, d-lactams having one or two b-phenyls were readily obtained (23,24). Additionally, 10 % of NÀPh amide (24') was also formed, which can be generated by the Smiles-type rearrangement.…”