Electroactive Protecting Groups and Reaction Units, 6. - Titanium Enolate Radical Cations in Solution: Generation, Characterization, and Their Reactions

For the first time titanium enolate radical cations were characterized in cyclic voltammetry experiments. Preparative one‐electron oxidation of titanium enolates 1‐3 led to the formation of benzofurans B1‐B3 through mesolytic Ti‐O bond fragmentation to α‐carbonyl radical and a cationic titanocene(IV) species. With 1+·, the kinetics of the Ti‐O bond cleavage was investigated by fast scan cyclic voltammetry providing a first‐order rate constant k1=850 ± 50 s−1 in acetonitrile at room temperature. The titanium enolate radical cations 1+·, 3+·, 4+· and 5%% were characterized by EPR spectroscopy, qualifying these species as electrophilic radicals. This feature can be exploited in CC bond formation reactions such as the formal dimerization of 6 to 2,3‐dimethyl‐1,4‐diphenylbuta‐1,4‐dione D6, which takes place on stage of the radical cation 6+·.