VINYLALLENES .10. PREPARATION AND REACTIVITY OF VINYLALLENYL LITHIUM

Five substituted vinylallenes were metallated at -70°C with butyllithium in THF/ether (50/50). The resulting metal compounds react with alkyl halides under formation of vinylallenes, which are substituted at the terminal C atom of the allene. Functionalized vinylallenic compounds are also obtained by the reactions of the same metal compound with electrophiles (aldehydes, ketones, amides, CO2, etc.). The regio-selectivity of these reactions is dramatically increased if the metallation is rapid (2 to 6 min) and, in several cases, if one equivalent of HMPT is added to the solution of the metal compound. Some conclusions concerning the reactivity of vinylallenyllithium and of vinylallenyl anions are drawn from the results. © 1979.