Synthesis of 3-ethoxy-4,4-diisopropyl-1,2-dioxetanes bearing a benzo(b)furan-2-yl or a benzo(b)thiophen-2-yl group: CIEEL-active dioxetanes emitting red light

Low-temperature singlet oxygenation of 1-ethoxy-2, 2-diisopropylethylenes substituted with a benzo(b)furanyl or a benzo(b)thiophenyl group bearing a t-butyldimethylsiloxy at the 5-, 6- or 7-position of the aromatic ring afforded the corresponding 1, 2-dioxetanes in moderate to high yields. On treatment with tetrabutylammonium fluoride in DMSO, dioxetanes with a trigger (siloxy group) at the 5- or 7-position of the aromatic ring decomposed to emit red light (lambda(max) = 615-628 nm), irrespective of the aromatic ring being benzofuran or benzothiophene. For both series of benzofuran-analogues and benzothiophene-analogues, an 'odd/even' relationship between the position of an oxyanion on the aromatic ring relative to the attachment point to the dioxetane and the chemiluminescent properties, lambda(max), Phi(CL), and t(1/2), is observed, as in the case for dioxetanes bearing a phenolic or naphtholic substituent.