One-pot three-component synthesis of stable pyrrole-3-selones using propargyl amines, acyl chlorides, and elemental selenium

Stable pyrrole-tailored selones, 1,2,5-trisubstituted-1,2-dihydro-3<i>H</i>-pyrrole-3-selones, have been synthesized in up to 75% yield from aminoacetylenic ketones and elemental selenium (KOH/EtOH, room temperature, 10-11 h). The work is mainly focused on the one-pot synthesis of these compounds (50-75% yields). This synthesis has been achieved <i>via</i> the reactions of propargyl amines with acyl chlorides in the presence of a Pd/Cu catalyst (toluene, 40-45 °C, 2-3 h) followed by the addition of a pre-heated mixture of Se/KOH (SnCl₂)/EtOH at room temperature. Our quantum-chemical calculations predict an exceptionally large ground-state dipole moment of about 7.6 Debye and an anomalously low vertical ionization energy of about 6.5 eV for the molecules under study. According to our calculations, these remarkable properties are due to the fact that the CSe bond is incorporated into the common π-system of the 3<i>H</i>-pyrrole ring, allowing charge transfer from N to Se. The latter effect also contributes to the exceptional stability of the reported selones.