Iron‐Promoted Radical Cyclization of β, γ‐Unsaturated Oximes: Dual Role of Iron(III) Nitrate as a Promoter and Nitrooxy Source

Abstract

A method for the radical cyclization of β,γunsaturated oximes to access the isoxazoline backbone has been developed, in which iron(III) nitrate plays a dual role as a promoter and a nitrooxy source. Iron-promoted cyclization is well tolerated with a series of aryl-and alkyl-substituted β,γ-unsaturated oximes, which readily affords the desired isoxazolines that can be easily transformed into useful compounds. Mechanistic experiments support that a radical pathway may be involved in the cyclization of β,γ-unsaturated oximes.

Iron-catalyzed domino coupling reactions of π-systems

“…Following an iminyl radical-mediated intramolecular 1,5-cyclization, the subsequent alkyl radical could propagate across carbon monoxide, eventually terminating with an alkyl or aryl amine. In the following year, the Li group described an interesting radical cyclization of β,γ-unsaturated oximes using iron(III) nitrate at a 50% catalytic loading in which the catalyst also acted as a source of nitrate ions for the reaction [ 140 ]. Upon oxidation of the alkyl radical, the Fe(III) species is reduced to Fe(II) releasing a nitrate anion which attacks the now electrophilic carbocation for a net iminyl-nitrooxylation reaction [ 140 ].…”

Palladium-Catalyzed β-C(sp3)–H Nitrooxylation of Ketones and Amides Using Practical Oxidants

“…10,17 Facile removal of the auxiliary was achieved by treating the nitrooxylation product 2j with 4 M HCl in 1,4-dioxane and water at 80 °C, providing βnitrooxylated free ketone 2j′ in 60% yield. 18 Moreover, nitrate esters could serve as precursors to the corresponding alkyl alcohols (see SI).…”