Degradative Alcohol Functionalization by Titanocene Photocatalysis

Organotitanium complexes are scarcely employed in photocatalytic reactions despite their robust ligand-to-metal charge-transfer photo-chemistry. Herein, we describe the development of titanocene pho-tocatalysis 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 alkoxyl radical and β-scission to carbon-centered radical, which is quenched through hydrogen atom transfer from an aryl thiol co-catalyst. 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, indi-cating generality of this mechanism in degradative functionalization of alcohols.