Reductive and oxidative alkylations involving free radical chain reactions

New free radical chain alklations of [alpha],[beta]-unsaturated carbonyl compounds with alkylmercury halides have been discovered. Although educt radicals of the enolyl type are unreactive towards alkylmercury halides, chain propagating reactions invovling electron transfer can be promoted by the presence of bases or iodide ion to yield respectively the oxidative (substitutive) and reductive (additive) alkylation products. In the presence of 1,4-diazabicyclo(2.2.2) octane the intermediate enolyl radical formed by the addition of a free radical to a 1,4-enedione can be deprotonated to a radical anion which yields the oxidative alkylation product upon electron transfer to alkylmercury halide. The electron transfer process regenerates the chain propagating alkyl radical. For the reductive alkylation, I[superscript]- or I[superscript]-/S[subscript]2O[subscript]8[superscript]2- promotes the photostimulated reductive alkylation of [alpha],[beta]-unsaturated carbonyls or 1,4-enediones. The effectiveness of alkylmercurials in the enolyl to enolate conversion decreases in the sequence of t-BuHgI/I[superscript]- ≥ BuHgCl/I[superscript]- \u3e t-BuHgI \u3e t-BuHgCl. The measured initial kinetic chain length for the reaction of t-BuHgI with N-methylmaleimide to give 3-(1,1-dimethylethyl)-1-methyl-2,5-pyrrolidinedione is ~200. The relative reactivities of [alpha],[beta]-unsaturated carbonyls, 1,4-enediones, [alpha],[beta]-unsaturated nitriles, imines, N-but-3-enyl-N-methylaminobenzene, and the benzene ring of the benzoyl group towards tert-butyl radical addition have been determined in competitive reactions. In the presence of para-toluenesulfonic acid or trimethylsilyl iodide the reactivity of imines is enhanced towards tert-butyl radical addition. Substitution reaction of aromatic compounds which have an electron-withdrawing group, such as benzaldehyde, produces exclusively the para-alkylation product via addition of the tert-butyl free radical. Radical cyclization is observed with 1-phenyl-4-penten-1-one and N-but-3-enyl-N-methylaminobenzene which is initiated by radical addition to the terminal alkene position followed by cyclization with the aromatic ring