PHOTOCHEMICAL-REACTIONS OF MERCAPTO AMINO SUBSTITUTED ALKYL PHENYLGLYOXYLATES INDUCED BY INTRAMOLECULAR ELECTRON-TRANSFER/

2'-Alkylthio ethyl phenylglyoxylates (1) and 2'-dimethylamino ethyl ph enylglyoxylate (10) were synthesized and their photochemistry studied. In contrast to their oxygen analogs 3, which give normal Norrish type II cleavage products, the title compounds undergo intermolecular elec tron transfer fi-om the heteroatum (sulfur/nitrogen) to the excited ca rbonyl group, followed by proton transfer and subsequent closing of th e resulting biradicals to produce seven-membered (2)/five-membered (11 ) lactones in high yield. Thiadialkyl phenylglyoxylates (9) react inef ficiently due to intramolecular self-quenching of phenylglyoxylate chr omophores. The photoreactivity of alpha-oxothioester (14) was compared with that of its nitrogen (alpha-oxoamide) and oxygen (phenylglyoxyla te) counterparts. (C) 1997 Elsevier Science Ltd.