Synthesis of 1-(3-tert-butyldimethylsiloxy)phenyl-5,5-dimethyl-2,7,8-trioxabicyclo[4.2.0]octanes: new dioxetanes giving high chemiexcitation yields in thermolysis and in fluoride-induced CIEEL-decay

Dioxetanes with annelated six-membered ring, 1-(3-tert-butyldimethylsiloxy)phenyl-5,5-dimethyl-2,7,8-trioxabicyclo[4.2.0]octanes (2a–2c) were synthesized by singlet oxygenation of the corresponding aryl-substituted dihydropyrans (3). Thermolysis of 2a–2c gave the corresponding ketoesters (5a–5c) as a normal decomposition product together with a considerable amount (23–26%) of ester (6) derived from Norrish type I reaction of the triplet-excited ester (5). On the other hand, treatment with tetrabutylammonium fluoride (TBAF) in DMSO induced rapid decomposition of 2 to emit blue light in high chemiexcitation yield (72–75%) of the oxyanion of a ketoester (10). These results show that the chemiexcitation efficiency of dioxetanes (2) was higher than that of their five-membered ring analog (1) not only for thermolysis and but also for the base-induced CIEEL.