Oxidative cyclizations of oximes using hypervalent iodine reagents

Abstract

This account overviews oxidative cyclization reactions of aldoximes or ketoximes promoted by hypervalent iodine reagents. The oxidation of aldoximes by iodine(III) compounds generates nitrile oxides which can further react with appropriate substrates via intermolecular or intramolecular 1,3-dipolar cycloaddition reactions leading to a variety of nitrogen and oxygen heterocycles. Hypervalent iodine reagents can also react with ketoximes producing the corresponding heterocyclic products via intramolecular cyclization reactions. Recently, the oxidative cyclization reactions of aldoximes have been realized under catalytic conditions mediated by hypervalent iodine active species.

Synthesis of Oxazoline and Oxazole Derivatives by Hypervalent-Iodine-Mediated Oxidative Cycloaddition Reactions

“…The isoxazoline ring is present in many important heterocycles that are widely used in several areas of chemistry and biomedical sciences. [24][25][26]52 Hypervalent iodine reagents such as (diacetoxyiodo)benzene, [115][116][117][118][119][120][121][122][123][124][125][126][127][128][129] [hydroxy(tosyloxy)iodo]benzene, 130,131 iodosylbenzene, [132][133][134][135] [bis(trifluoroacetoxy)iodo]benzene, 136 (dichloroiodo)benzene, 137 and also in situ generated iodine(III) species, [138][139][140][141] can be used as efficient tools for construction of the isoxazoline ring.…”

“…The hypervalent-iodine-mediated oxidative cycloaddition of aldoximes with unsaturated substrates represents a powerful methodology for the synthesis of isoxazoline compounds. 52,[115][116][117][118][119][120][132][133][134]136,137 For example, the reactions of various aldoximes 54 with alkenes 55 and (diacetoxyiodo)benzene afford the corresponding isoxazolines 56 in generally high yields (Scheme 18). 116 The key intermediate in this reaction, nitrile oxide, is generated by oxidation of the aldoxime with (diacetoxyiodo)benzene, and then the generated nitrile oxide reacts with alkenes to produce the isoxazoline products.…”

“…Numerous classes of heterocyclic compounds have been prepared under mild conditions using hypervalent iodine reagents. [50][51][52] In the present review, synthetic approaches to the azole derivatives, oxazolines 1, oxazoles 2, isoxazolines 3, and isoxaz-oles 4 (Figure 1), starting from various substrates using hypervalent iodine species are summarized, and recent developments in chemical and electrochemical synthetic procedures toward these heterocycles are discussed.…”

Enantioselective 5-exo-Fluorocyclization of Ene-Oximes

“…Isoxazoline framework has been recognized as a significant substructure of natural and unnatural compounds [1,2], which possess various biological activities including anticancer activity [3,4], FXa inhibitory activity [5], and antiparasitic activity [6,7,8,9]. Therefore, the construction of isoxazoline has been actively studied [10,11,12,13]. Among various methods for isoxazoline synthesis, a difunctionalization-type cyclization of ene-oxime is one of the major strategies.…”

Iodonium Salts as Benzyne Precursors

“…Organohypervalent iodine compounds are known as efficient, versatile reagents that have been widely used in the various oxidative transformations . One of the most important classes of organohypervalent iodine compounds is represented by hypervalent aryliodonium species, which have found wide use for various new bond‐forming reactions such as carbon–carbon, carbon–heteroatom, or heteroatom–heteroatom bond formation.…”