Diastereoselective heterocyclization of geminal bromo-fluoro arylcyclopropanes by nitrosonium tetrafluoroborate: Access to 4-fluorinated isoxazolines and isoxazoles

摘要

A series of 5-aryl-4-bromo-4-fluoroisoxazolines was synthesized via nitrosation of 2-aryl-1-bromo-1- fluorocyclopropanes with NOBF4. 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-fluoroor 5-aryl-4-bromoisoxazoles in good yields in the reaction with Lewis acids. (C) 2019 Elsevier Ltd. All rights reserved.