Photochemische Reaktionen 45. Mitteilung. α-Sulfonyloxyketone: Sterische Voraussetzungen für die photolytische RSO3-Elimination – Nachweis von kationischen Produkten Vorläufige Mitteilung

Upon irradiation in the n→* transition, the 2, 5-cis tosyloxyketone 9 reacted readily to give the cyclohexenone 11 in benzene solution, and a 4:1 mixture of products 11 and 12 in dioxane solution, while the 2, 5- trans isomer 10 remained almost photostable under comparative conditions. Prolonged irradiation of 10 afforded only small amount of products 11 and 12 in an approximate 1:1 ratio. It is concluded that for the photolytic elimination of the tosyloxy group a non-eclipsed conformation of the CO and the C_α O bonds, as already present in the ground state of compound 9 , is required. When 9 was irradiated in aqueous dioxane solution, the β-hydroxy-ketone 13 was formed in addition to 11 . Similarly, the photochemical conversion of the aliphatic tosyloxyketone 5 to the unsaturated ketone 6 was largely suppressed in aqueous dioxane, and the hydroxyketone 15 was formed instead. These results are evidence for the intervention of cationic intermediates in the pathways leading to the rearranged products 11 and 15 , and hence point to a heterolytic mode of photocleavage.