ARENE-CATALYZED LITHIATION OF 1,4-DICHLOROBUT-2-ENES AND 3,4-DICHLOROBUT-1-ENE AND REACTION WITH ELECTROPHILES - A COMMON REACTION PATHWAY

The reaction of (Z) or (E)-1,4-dichlorobut-2-ene (1,2) or 3,4-dichlorobut-1-ene (3) with an excess of lithium powder and a catalytic amount of 4,4'-di-tert-butylbiphenyl (5 mol %) in the presence of an electrophile [(CH2)(4)CO,Bu(t)CHO,Me(3)SiCl] in THF at 0 degrees C yields, after hydrolysis, the corresponding 1,4- and 1,2-disubstituted compounds (Z/E)-4 and 5, the ratio of them being independent on the starting material. In the case of compounds 4 the Z-diastereomer is largely the major one. When dichlorodiethylsilane was used as electrophile the corresponding substituted silacyclopentene 6 was the only reaction product isolated. A possible mechanism involving dilithiated species is proposed.