Organic Photochemical Reactions. XXVI. Photoaddition of Singlet and Triplet Methyl Pyruvate with 2,3-Dimethyl-2-butene

UV irradiation of methyl pyruvate in the presence of 2,3-dimethyl-2-butene leads to the formation of four primary photo-products in reasonable quantum yield: two unsaturated ethers (1and 2) and two unsaturated alcohols (3and 4). The effects of olefin concentration on the quantum yield of product formation, as well as quenching studies, suggest that 3and 4are formed from the excited singlet state of methyl pyruvate, while 1and 2are produced from the triplet state of methyl pyruvate. The role of exciplexes in this reaction is discussed. Quenching data of fluorescence of methyl pyruvate and the kinetic analysis of this reaction support these considerations.