Several mechanistic alternatives proposed for the photochemical deprotection of dimethoxybenzoin esters are presented. Both experimental and theoretical evidence suggest the mechanism is heterolysis of the singlet excited state to form a carboxylate and the α-ketocation. The α-ketocation has been observed by transient spectroscopy. We propose the α-ketocation undergoes electrocyclization to an intermediate with extended conjugation, whose deprotonation gives the observed benzofuran product. A Brønsted study of the rates of benzofuran formation with dimethoxybenzoin esters derived from acids of varying pK_a shows the rate is independent of the basicity of the leaving group. In this multistep reaction, benzofuran formation by a final deprotonation is slower than α-ketocation generation.