Radical Cascade Reactions of β,γ‐Unsaturated Hydrazones/Oximes

Abstract

Radical cascade cyclization of β,γ‐unsaturated hydrazones/oximes has recently emerged as an efficient and powerful protocol for the construction of diverse and valuable functionalized pyrazolines and isoxazolines. In this review, three catalytic ways of radical cascade cyclization of β,γ‐unsaturated hydrazones/oximes are summarized and classified; these are transition‐metal‐catalyzed systems, transition‐metal‐free systems, and photo‐/electrocatalytic systems, respectively. Through these methods, various functional groups are installed on the pyrazoline and isoxazoline skeletons to enrich the small organic molecule library.

Oxy‐/Amino‐Difluoromethylthiolation of Alkenes: Synthesis of HCF2S‐Containing Isoxazolines and Pyrazolines

“…They also serve as versatile synthesis intermediates in organic synthesis. Among the methods for constructing isoxazolines and pyrazolines, straightforward difunctionalization of β,γ‐unsaturated oximes/hydrazones has attracted considerable attention because such transformation could introduce a group on the C−C double bond while constructing the azoline skeleton [16–18] . Although great efforts have been devoted to difunctionalization of β,γ‐unsaturated oximes/hydrazones, developing efficient approaches to isoxazolines and pyrazolines bearing important functionalities is still highly desired.…”

Synthesis of 3‐Acyl‐Isoxazoles via Radical 5‐endo trig Cyclization of β,γ‐Unsaturated Ketones with NaNO2

“…[10] Efforts toward the development of novel methods have been continuing to grow unabated. [11] Since the first discovery of radical 5-exo trig cyclization of β,γ-unsaturated oximes was reported by Han in 2012, [12] recent years have witnessed the development of some practical methods for the synthesis of various functionalized isoxazolines [13] from β,γunsaturated oximes, which could be easily prepared from β,γunsaturated ketones. [14] In addition, the synthesis of 3,5-diarylisoxazoles from α,β-unsaturated oximes by 5-endo trig cyclization has also been reported widely.…”

Divergent Synthesis of 3,5‐Disubstituted Pyrazoles and α, β‐Alkynic Hydrazone from Diarylpropynones and Carbazates

“…Despite the great progress made, [8][9][10][11][12][13] there still exists a great demand to develop efficient methodologies for the synthesis of substituted pyrazoles.…”

“…[14] Thus, this approach could be a promising alternative to 1,3-dipolar cycloaddition for the regioselective synthesis of 3,5-disubstituted pyrazoles. To the best of our knowledge, in addition to alkali [8] or metal [10] catalyzed synthesis of pyrazole rings, the use of Lewis acids catalysis has also received some attention with tosylhydrazones as synthons [15] (Scheme 1c). In connection with continuing efforts in research into Lewis-acid-catalyzed synthesis of nitrogen heterocycles, [16] we herein reported the Yb(OTf) 3 -catalysed cyclization of diarylpropynones with methyl carbazate (Scheme 1 d).…”