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A new method for the synthesis of 3-aryl-5-fluoroisoxazoles via the reaction of nitrosonium chlorosulfate with 2-aryl-1-bromo-1-fluorocyclopropanes containing acceptor substituents in the aromatic ring has been developed. The reaction proceeds highly regioselectively thus providing 3-aryl-5-fluoroisoxazoles in good yields. The structure of isoxazoles was corroborated by the DU8+ hybrid DFT/parametric computational approach. Image 1 • Access to 5-fluoroisoxazoles from geminal bromofluoroarylcyclopropanes. • High regioselectivity ensures good yields of 5-fluoroisoxazoles. • DU8+ hybrid DFT/parametric computational approach is fast and accurate method for confirmation of compound structure. [ABSTRACT FROM AUTHOR]

Abstract: Nitrosation of di(gem-dichlorocyclopropane) with NOCl·2SO3 proceeds regiospecifically and in two stages to afford di(5-chloroisoxazol-3-yl). The introduction of a methyl group on one of the cyclopropane rings crucially influences the reactivity and mode of transformation of the substrate, leading to 3-chloro-5-methyl-5-(1,3,3-trichloroprop-2-en-1-yl)isoxazoline, the structure of which was established by X-ray single crystal diffractometry. [Copyright &y& Elsevier]

An efficient transformation of 2-aryl-1,1-dibromocyclopropanes under the action of sulfur trioxide activated nitrosyl chloride has been developed, providing a series of arylated 5-bromoisoxazoles with good yields. It is noteworthy that under the reported conditions the nitrosation–heterocyclization reaction proceeded with high regioselectivity leading exclusively to 3-aryl-5-bromoisoxazoles. [ABSTRACT FROM AUTHOR]

A series of 5-aryl-4-bromo-4-fluoroisoxazolines was synthesized via nitrosation of 2-aryl-1-bromo-1-fluorocyclopropanes with NOBF 4. It was shown that the E -isomers of the cyclopropanes react highly regio- and diastereoselectively leading exclusively to the E -isomers of the isoxazolines. The obtained 5-aryl-4-bromo-4-fluoroisoxazolines were transformed selectively into the corresponding 5-aryl-4-fluoro- or 5-aryl-4-bromoisoxazoles in good yields in the reaction with Lewis acids. Image 1 • Access to 4-fluorinated isoxazolines from gem -bromofluoroarylcyclopropanes. • High regio- and diastereoselectivity for E -4-bromo-4-fluoroisoxazolines. • Highly selective silver nitrate assisted dehydrobromination to 4-fluoroisoxazoles. • Highly selective AlCl 3 assisted dehydrofluorination to 4-bromoisoxazoles. [ABSTRACT FROM AUTHOR]