Photochemical reactions of mercapto/amino substituted alkyl phenylglyoxylates induced by intramolecular electron transfer

• Published in: Tetrahedron Vol. 53; no. 8; pp. 2751 - 2766
• Main Authors: Hu, Shengkui, Neckers, Douglas C.
• Format: Journal Article
• Language: English
• Published: OXFORD Elsevier Ltd 24.02.1997; Elsevier
• Subjects: Amino; Chemistry; Chemistry, Organic; Electron Transfer; Mercapto; Phenylglyoxylates; Photochemical; Physical Sciences; Science & Technology; Phenylglyoxylates; Amino; Mercapto; Photochemical; Electron Transfer; DITERPENES; ORGANIC-SYNTHESIS; ACID; photochemical; MOLECULAR PHOTOCHEMISTRY; CONFIGURATION; phenylglyoxylates; RADICAL CHAIN REACTIONS; mercapto; PHOTOREACTIONS; amino; electron transfer; FLUORESCENCE; REDUCTION; CHARGE-TRANSFER INTERACTIONS
• ISSN: 0040-4020; 1464-5416
• DOI: 10.1016/S0040-4020(97)00044-6

2′-Alkylthio ethyl phenylglyoxylates ( 1) and 2′-dimethylamino ethyl phenylglyoxylate ( 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 electron transfer from the heteroatom (sulfur/nitrogen) to the excited carbonyl group, followed by proton transfer and subsequent closing of the resulting biradicals to produce seven-membered ( 2)/five-membered ( 11) lactones in high yield. Thiadialkyl phenylglyoxylates ( 9) react inefficiently due to intramolecular self-quenching of phenylglyoxylate chromophores. The photoreactivity of α-oxothioester ( 14) was compared with that of its nitrogen (α-oxoamide) and oxygen (phenylglyoxylate) counterparts. These title compounds cyclize efficiently to lactones of different ring sizes.