Abstract
The enantioselective 5-exo-fluorocyclization of ene-oxime compounds was demonstrated under phase-transfer catalysis. Although deprotonative fluorinations competed, the chemical yields and the ee values of the desired isoxazoline products were generally moderate to good. The absolute stereochemistry of the major isomer was determined to be S by comparison with the literature after transformation of the product to the corresponding iodinated isoxazoline.
Highlights
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]
Fluorine chemistry has contributed to pharmaceutical and agrochemical sciences, because an introduction of fluorine atom(s) at an appropriate position often improves the property of the parent compounds in terms of metabolic stability, lipophilicity, and so on [22,23,24,25,26,27]
We report our effort to the catalyst seems essential, because the intramolecular cyclization step is an enantio-determining develop the enantioselective 5-exo-fluorocyclization of ene-oximes to provide fluorinated isoxazolines step
Summary
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]. We recently developed a linked-binaphthyl dicarboxylic acid precatalyst 1, which was proven to be highly effective for the asymmetric fluorocyclization and the deprotonative fluorination of allylic amides (Scheme 1a) [40,41]. In these reactions, hydrogen bonding between the catalyst and the substrate was considered to be crucial for high asymmetric induction. We report our effort to the catalyst seems essential, because the intramolecular cyclization step is an enantio-determining develop the enantioselective 5-exo-fluorocyclization of ene-oximes to provide fluorinated isoxazolines step.
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