The synthesis of the highly reactive 1,4-unsymmetrically substituted butatrienes 12a-c is described. When employing a strict synthetic protocol, these alkatrienes react with lithium metal to 3,4-dilithio-1,2-butadienes 20a-c as stable intermediates. The structure of 20 is supported by IR and NMR spectroscopic evidence. The same dianionic intermediate can be prepared in one case by double deprotonation
The reaction of various cyclic and acyclic alkynes with lithium dust (2% sodium) to form vicinal dilithioalkenes has been investigated: Aliphatic alkynes, e.g. 3-hexyne (27a), exclusively afford the corresponding (E)-dilithioalkenes, insoluble solids which are stable at room temperature and allow access to a variety of tetrasubstituted olefins in acceptable yields