1,3-Dichloro-2-butene: a useful precursor for the 2-butene-1,3-dianion and its corresponding 1,3-dipolar synthon

The reaction of 1,3-dicloro-2-butene (; 5:1 Z:E-mixture) with lithium powder and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 1% molar) in the presence of different electrophiles [EtCHO, PriCHO, ButCHO, c-C6H11CHO, Me2CO, Et2CO, (CH2)4CO, (CH2)5CO, (c-C3H5)2CO, Me3SiCl] in THF at temperatures ranging between −78 and −50°C gives, after hydrolysis with water, the corresponding products in different Z:E-ratios depending on the electrophile used. Treatment of some diols with hydrochloric acid gives dienic alcohols or substituted dihydropyrans , depending on the structure of the starting diol. Finally, the same dichlorinated starting material is transformed into the corresponding allylic amines derived from morpholine and benzyl methyl amine and submitted to the same DTBB-catalysed lithiation as above, so after reaction with different electrophiles [ButCHO, c-C6H11CHO, Me2CO, Et2CO, (CH2)4CO, (CH2)5CO, Me3SiCl] and final hydrolysis with water, compounds are isolated having a Z-configuration. A mechanistic explanation for this behaviour is given.