Synthesis of novel spiro[cyclopropane-indolizine] derivatives via magnesium-mediated conjugate addition of bromoform

The reaction of 6,7-dihydroindolizin-8(5H)-one and an aromatic aldehyde yielded (E)-7-(arylmethylene)-6,7-dihydroindolizin-8(5H)-ones which underwent addition of bromoform in the presence of magnesium under N2 to give a novel series of 3-aryl-2,2-dibromo-5′H-spiro[cyclopropane-1,7′-indolizin]-8′(6′H)-one derivatives. The structures of the products were established by 1H NMR, 13C NMR, IR spectroscopy and mass spectra.