Hemin-Catalyzed Oxidative Phenol-Hydrazone [3+3] Cycloaddition Enables Rapid Construction of 1,3,4-Oxadiazines

Abstract

Herein, we present a hemin-catalyzed oxidative phenol-hydrazone [3+3] cycloaddition that accommodates a broad spectrum of N-arylhydrazones, a class of less exploited 1,3-dipoles due to their significant Lewis basicity and weak tendency to undergo 1,2-prototropy to form azomethine imines. It renders expedient assembly of diversely functionalized 1,3,4-oxadiazines with excellent atom and step economy. Preliminary mechanistic studies point to the involvement of a one-electron oxidation pathway, which likely differs from the base-promoted aerobic oxidative scenario.

Particulate matter exposure is highly correlated to pediatric asthma exacerbation

“…In vitro , PM was associated with increased release of cytokines, such as IL-33, IL-1, IL-6, and IL-8 [ 25 – 27 ]. But in vivo , the relationship between PM and the release of associated cytokines remains uncertain [ 28 ]. Our study revealed that the airway inflammatory response aggravated by PM intervention was accompanied by elevated expression of IL-33.…”

Update on the Synthesis of N‐Heterocycles via Cyclization of Hydrazones (2017–2021)

“…Mechanistically, intermediate 279 is obtained from the silver-catalyzed cyclization of N'-( 2 In the same year, Wu and Zhong developed a mild, valuable strategy for synthesis of 1,3,4-oxadiazines 285 via hemin-catalyzed cycloaddition of phenol hydrazones [3 + 3] (Scheme 44). [77] This method is characterized by mild conditions, easy availability of all starting materials, good substrate universality, high yields, and excellent atomic and step economy. Obviously, a variety of hydrazones with different electron-withdrawing or electron-donating substituents can be used in this reaction to offer the desired products with moderate to excellent yields.…”

Recent advances in catalytic oxidative reactions of phenols and naphthalenols

“…Preliminary mechanistic studies pointed to the involvement of a one-electron oxidation pathway, which likely differed from the base-promoted aerobic oxidation scenario (Scheme 13). 93 Zhang et al developed the Pd(II)-catalyzed chemoselective intermolecular 1,2-oxyamination and 1,2-aminooxygenation of conjugated dienes 32 to afford 2-and 3-functionalized 1,4-benzoxazine derivatives 33 and 34, respectively. The reaction proceeded via the in situ generation of o-quinone monoimines from 31.…”

“…Preliminary mechanistic studies pointed to the involvement of a one-electron oxidation pathway, which likely differed from the base-promoted aerobic oxidation scenario (Scheme 13). 93…”