Generation of nitroalkanes, hydroximoyl halides and nitrile oxides from the reactions of β-nitrostyrenes with Grignard or organolithium reagents

Abstract

The β-nitrostyrenes 1 or 2 react with Grignard or organolithium reagents in ether or THF solution to generate by 1,4-addition the intermediate nitronates A. When A is treated with dilute hydrochloric acid, high yields of the nitroalkanes 3 (and oximes 4) or 5 are obtained. Hydroximoyl halides 6, 8 or nitrile oxides 7 can be isolated when the intermediate A is slowly added to the ice cold concentrated hydrohalic acid. The same products 6 and/or 7 are observed if the nitronates, generated from the substrate 1a, are added to 85% aqueous H 2SO 4 but only the hydrolyzed carboxylic acids 9 are generated when the β-nitrostyrenes 2 are reacted with Grignard reagents and worked up under the same condition. The nitrile oxides 7 can undergo 1,3-dipolar cycloaddition with alkenes or alkynes to generate 2-isoxazolines or isoxazoles. A one-pot synthesis of the [n,3,0] bicyclic (n = 3 or 4) compounds 23–27 by intramolecular nitrile oxide-olefin cycloadditions is reported.