Photostimulated Nucleophilic Aromatic Substitution for Halides with Carbon Nucleophiles. Preparative and Mechanistic Aspects

The photo-S_RN1 reaction operates efficiently with enolate anions derived from simple ketones and esters, but 2-lithio-1,3-dithiane gives low yields. The sluggish and inefficient reaction of dialkyl-substituted ketone and ester enolates is traced to hydrogen atom transfer from the carbon adjacent to the enolate anion to the transient phenyl radical. The first systematic survey of intramolecular coupling of ketone enolate anions shows that six-, seven-, eight-, and ten-membered rings can be formed, although the ß-hydrogen transfer becomes important in certain cases.