Photolysis of 1,2:3,4-di-O-isopropylidene-6-O-(p-tolylsulfonyl)-α-D-galactopyranose (5) in methanol under nitrogen in the presence of sodium hydroxide or diazabicyclo[2.2.2]octane (3, DABCO) produces toluene and 1,2:3,4-di-O-isopropylidene-α-D-gatactopyranose (6). Electron transfer from DABCO or hydroxide ion to singlet excited5to generate a radical anion is the first step in this reaction. The radical anion rapidly fragments to give thep-tolylsulfonyl radical (2) and deprotonated6, which accepts a proton from the solvent. Thep-tolylsulfonyl radical (2) then abstracts a hydrogen atom from the solvent to givep-toluenesulfinic acid, a compound that is converted to thep-toluenesulfinate anion (8) under the basic reaction conditions. Photolysis of8completes the reaction sequence by forming toluene.