Photochemical reaction of 2,2′-pyridyl — cis-enediol formation in ethers

✍ Scribed by Hiroyasu Inoue; Tadamitsu Sakurai; Toshihiko Hoshi; Jun Okubo

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 579 KB
• Volume: 72
• Category: Article
• ISSN: 1010-6030
• DOI: 10.1016/1010-6030(93)85083-k

✦ Synopsis

In ethers, such as tetrahydrofuran and 1,4-dioxane. 2,2'-pyridyl (di-Zpyridyl diketone) is photochemically reduced lo the cis-enediol-type compound (cir-1,2-di(Z-pyridyI)-1,2-ethenediol), in contrast with the previously reported trans.enediol formation in alcohols, etc. This solvent dependence of the photochemical behaviour can be interpreted in terms of the difference in the reactive excited states of 2,2'-pyridyl in the two photochemical reactions. Investigations of the external heavy atom effect, triplet quenching experiments and the initial concentration dependence of the substrate indicate that cb-enediol is preferentially formed via the lowest excited singlet state of 2,2'-pyridyl in ethereal solutions, whereas the lowest excited triplet state participates in frans-enediol formation in alcohols, etc. From the isotope effects observed in deuterated tetrahydrofuran and ethanol, the initial step in the photoreactions, ie. hydrogen atom abstraction or electron transfer, is briefly discussed.