Anion radical [2 + 2] cycloaddition as a mechanistic probe: stoichiometry- and concentration-dependent partitioning of electron-transfer and alkylation pathways in the reaction of the Gilman reagent Me2CuLi.LiI with bis(enones).

Exposure of easily reduced aromatic bis(enones) 1a-1e to the methyl Gilman reagent Me(2)CuLi.LiI at 0 degrees C in tetrahydrofuran solvent provides the products of tandem conjugate addition-Michael cyclization, 2a-2e, along with the products of [2 + 2] cycloaddition, 3a-3e. Complete partitioning of the Gilman alkylation and [2 + 2] cycloaddition pathways may be achieved by adjusting the loading of the Gilman reagent, the rate of addition of the Gilman reagent, and the concentration of the reaction mixture.

Chemically induced anion radical cycloadditions: intramolecular cyclobutanation of bis(enones) via homogeneous electron transfer.

The first examples of anion radical cycloaddition induced by homogeneous electron transfer from chemical agents are described. Specifically, upon exposure to chrysene anion radical, bis(enone) substrates are found to engage in stereoselective intramolecular [2 + 2] cycloaddition. These studies, along with the corresponding electrochemically initiated reactions, provide insight into this fundamentally new pattern of reactivity and support the feasibility of expanding this novel reaction type.

Anion radical chain cycloaddition of tethered enones: intramolecular cyclobutanation and Diels-Alder cycloaddition.

[reaction: see text] The anion radicals of certain bis(enones), generated by cathodic reduction, are observed to participate in intramolecular cyclobutanation, yielding bicyclo[3.2.0]heptane derivatives through an anion radical chain mechanism.

Mechanistic Distinctions between Cation Radical and Carbocation Propagated Polymerization.

The polymerization of bis[4-(1-propenyl)phenyl] ether in the presence of tris(4-bromophenyl)aminium hexachloroantimonate is found to occur by competing cation radical and carbocation pathways. These pathways involve, respectively, cyclobutanation and linear addition. Methods for favoring each mechanistic type are proposed and explored.