Substrate oriented selectivity in the Mg-mediated conjugate addition of bromoform to electron deficient alkenes

The Mg-mediated conjugate addition of bromoform to a variety of electron deficient alkenes has been investigated. In the case of nitrodienes and dibenzylideneacetones, the tribromomethylated products were isolated, whereas spiro-cyclopropanated products were obtained with cyclic dibenzylideneketones and 3-olefinic oxindoles. The spiro-cyclopropyl ketones derived from cyclic dibenzylideneketones were successfully transformed to fused furans via Cloke-Wilson rearrangement.