Cydoadditions of Trifluoroacetonitrile Oxide with Olefins and Acetylenes

Abstract
The regio- and stereoselectivity of the cydoadditions of trifluoroacetonitrile oxide (1) with olefins and acetylenes were described. The oxide 1, generated in situ from trifluoroacetohydroximoyl bromide etherate in the presence of triethylamine, reacted with various monosubstituted olefins and acetylenes to give exclusively 5-substituted 3-trifluoromethyl-2-isoxazolines and -isoxazoles, respectively, whereas 1 cyclized with 1,2-disubstituted olefins and acetylenes to result in the formation of a mixture of two regioisomeric products. On the other hand, the cycloaddition of 1 with (Z)-β-methylstyrene afforded a mixture consisting of two regioisomeric isoxazolines retaining Z-configuration and one diastereoisomeric isoxazoline.