Photochemical Reactions of Halo-/Aryl Sulfide-Substituted Alkyl Phenylglyoxylate, an Assessment of the Lifetime of the Intermediate 1,4-Biradical

Photochemical reactions of several halo/aryl sulfide-substituted alkyl phenylglyoxylates ( 1 ) were studied. For 2‘-bromo- ( 1b ), 2‘-iodo- ( 1c ), 2‘-(phenylthio)- ( 1d ), and 2‘-(phenylsulfinyl)- ( 1e ) ethyl phenylglyoxylate, vinyl phenylglyoxylate ( 2 ), proposed to be the result of β-elimination from the 1,4-biradical formed by triplet state γ-hydrogen abstraction, is the dominant photoproduct. In the cases 1b and 1d Norrish Type II products were also observed. Vinyl phenylglyoxylate ( 2 ) was not observed with 2‘-chloroethyl ( 1a ), 3‘-bromopropyl ( 1f ), and 3‘-(phenylthio)propyl ( 1g ) phenylglyoxylate. The lifetime of the 1,4-biradical intermediate is deduced from the competition between the β-elimination of the monoradical and the normal biradical decay. The triplet lifetime and the photoreaction efficiency of 1 were not significantly affected by halogen-substitution.