Degradative Alcohol Functionalization by Titanocene Photocatalysis

Organotitanium complexes are scarcely employed in photocatalytic reactions despite their robust ligand-to-metal charge-transfer photochemistry. Herein, we describe the development of titanocene photocatalysis for the carbon–carbon bond cleavage functionalization of alcohol substrates. Mechanistic studies are consistent with in situ generation of a photoactive titanium alkoxide followed by subsequent photogeneration of an alkoxyl radical and β-scission to a carbon-centered radical, which is quenched through hydrogen atom transfer from an aryl thiol cocatalyst. A variety of alcohols, including pharmaceutical compounds, can be effectively cleaved in this fashion to the requisite carbonyl and hydrocarbon fragments. Furthermore, the catalytic manifold is employed in cyanation and chlorination reactions, indicating the generality of this mechanism in the degradative functionalization of alcohols.