Synthesis of Chromeno[4,3‐<i>b</i>]pyrrol‐4(1<i>H</i>)‐ones, from β‐Nitroalkenes and 4‐Phenylaminocoumarins, under Solvent–free Conditions

Abstract

Abstract A new approach toward chromeno[4,3‐ b ]pyrrol‐4(1 H )‐ones, by annulation of 4‐phenylaminocoumarins with β‐nitroalkenes, is reported and its conditions were optimized. The transformations under the fine‐tuned conditions took place under promotion by TsOH.H 2 O, in the absence of solvent. The scope and limitations of the process were explored, by systematic modification of two diversification points. A reaction mechanism, triggered by a Michael addition of the nitrogen moiety of the 4‐phenylaminocoumarins to the β‐nitroalkene, was also proposed. Further functionalization of a selected tricycle was performed; the photophysical (UV and fluorescence spectra; 1 O 2 generation) and electrochemical (cyclic voltammetry) properties of some heterocycles were studied.