Michael additions versus cycloaddition condensations with ethyl nitroacetate and electron-deficient olefins.

Ethyl nitroacetate (1) reacts with electron-poor olefins in the presence of a base to give either the Michael adducts 3 or the isoxazoline cycloadducts 4, resulting from water elimination. The proportions of the two products depend on the reaction conditions and change in the course of the process. Kinetic profiles for the two reactions show that the cycloaddition-condensations require long induction times that dramatically decrease upon addition of a copper salt to the catalytic system: the drops in the induction time cause increases in the proportion of cycloadducts 4, which are often the sole reaction products. This is the first report on the selective formation of products 3 and 4 from primary nitro compounds through modulation of the catalytic system.