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
Titanacyclobutenes, readily prepared from Cp2TiCH2·Al(CH3)2Cl and alkynes, react with ketones and aldehydes to afford metallacyclic products resulting from insertion into either the titanium-alkyl or the titanium-vinyl bond of the titanacyclobutene. The latter insertion products are thermally unstable, undergoing facile retro [4+2] cycloaddition to afford substituted 1,3-dienes in good yield.