Abstract
AbstractThe Z‐syn‐locked 1,1′‐methylene‐2,2′‐pyrromethen‐5(1H]‐one 1, prepared in 45% yield in a one‐pot reaction from the previously reported 1,1′‐methylenebis(pyrrole‐5‐carbaldehyde) (8), exhibits a brilliant fluorescence with a high quantum yield (1.0) in contrast to the parent 2,2′‐pyrromethen‐5[1H]‐one systems. The λmax of emission and the quantum yield are solvent dependent. Catalytic reduction of 1 affords the 3,4‐dihydro derivative 2 in 80% and the 2,3,4,6‐tetrahydro derivative 3 in 80% and 95% yields, respectively. Compounds 2 and 3 exhibit no fluorescence, however 2 shows a very efficient photoFries‐type rearrangement. Advanced 1H NMR techniques had to be applied in order to obtain the complete analysis of the 1H NMR spectrum of 3, which showed the conformational details of its reduced bicyclic moiety.
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