REARRANGEMENT AND CATALYSIS IN THE SEYFERTH REACTION.

Article abstract of DOI:10.1021/ja00324a029

The Seyferth reagent PhHgCBr//3 reacts with trans-1,2-dichloroethene to give two major products, trans-1,1-dibromo-2,3-dichlorocyclopropane (C) and 1,1-dibromo-3,3-dichloropropene (P). The stereospecifically formed cyclopropane is consonant with a singlet carbene mechanism, but the rearranged propene requires a second intermediate. Observation that the concentration ratio left bracket P right bracket / left bracket C right bracket is inversely proportional to the concentration of the alkene demonstrates that there are two intermediates, that the cyclopropane comes from the first-formed intermediate, and that the propene comes from the second-formed intermediate.