Poronik Yevgen M, Gryko Daniel T
Institute of Organic Chemistry PAS, Kasprzaka 44/52, 01-224 Warsaw, Poland.
Chem Commun (Camb). 2014 Jun 1;50(43):5688-90. doi: 10.1039/c4cc01106f. Epub 2014 Mar 20.
An unexpected discovery of the novel cyclocondensation reaction of 1,8-diazabicyclo[5.4.0]undec-8-ene (DBU) and 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) with alkyl coumarin-3-carboxylates is described. First, an unknown skeleton is generated through the concomitant formation of new nitrogen-carbon and carbon-carbon bonds followed by the oxidation of the intermediate product by the second equivalent of the starting coumarin. Pentacyclic DBN-derivatives exhibit strong fluorescence both in solutions (Φfl∼ 0.6-0.8) and in the solid state, while non-planar DBU-derivatives exhibit strong fluorescence in the solid state only.
