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Synthesis of thermally stable acylamino-substituted bicyclic dioxetanes and their base-induced chemiluminescent decomposition.

Hydroxyaryl-substituted dioxetanes 2-4 fused with a pyrrolidine ring were selectively synthesized by singlet oxygenation of the corresponding dihydropyrroles 5-7. These N-acylamino-substituted bicyclic dioxetanes were quite stable thermally, and 2a and 2b were estimated to possess half-lives of 32 and 34 y at 25 degrees C. When treated with TBAF (tetrabutylammonium fluoride) in DMSO, these dioxetanes underwent charge-transfer-induced decomposition (CTID) to emit yellow-orange light. The chemiluminescence efficiencies Phi(CL) for dioxetanes 2 ranged from 10(-6) to 10(-2). On the other hand, dioxetane 4 bearing a 4-(benzothiazol-2-yl)-3-hydroxyphenyl moiety showed chemiluminescent decomposition with high efficiency (Phi(CL) = 0.15) comparable to its oxy-analogue 26. Prominent characteristics for CTID of the present dioxetanes were that the N-acylamino-group influenced the color of chemiluminescence as well as the rate of decomposition k(CTID), and furthermore an N-acyl substituent could decisively affect the singlet-chemiexcitation efficiency, as observed for the case of 2b.