Evidence against Single-Electron Transfer in the Additions of Most Organomagnesium Reagents to Carbonyl Compounds

A radical
clock system was developed to investigate single-electron
transfer (SET) in the reactions of organomagnesium reagents with carbonyl
compounds. The fluorenylcyclopropyl radical clock was selected because
it is the fastest known radical clock. Additions of Grignard reagents
to aldehydes or methyl ketones provided no evidence for ring-opened
products that would indicate reaction through SET. Additions of some
Grignard reagents to aromatic ketones, however, resulted in the formation
of ring-opened products, suggesting SET.