The Solvent Effect on the Reaction of 1,1,4,4-Tetraphenyl-2-halobuta-2,3-dien-1-ol with Mercuric Halide

The reaction of the title compound (I) with mercuric halide in an aprotic and in a protic solvent afforded the fulvene derivative (VII) and the dihydrofuran derivative (VIII or IX) respectively. Both the cross-reactions (bromo-analog of I (Ia)+HgCl2, chloro-analog of I (Ib)+HgBr2) in an aprotic solvent afforded the chloro-fulvene derivative (VIIb). However, when the above reactions were carried out in a protic solvent, the product was the dihydrofuran derivative (IX), in which the halogen combining with carbon is chlorine and that combining with mercury is bromine. On the basis of the results of those cross-reactions, the reaction mechanism will be discussed. Acetonitrile showed distinctive behavior. In acetonitrile, the bromine of Ia was easily exchanged with the chlorine of sodium chloride at room temperature, and Ib was obtained quantitatively.