Allenes, Acetylenes and Dienes

More recently, allenes, acetylenes and activated dienes have been added as olefin equivalents, leading to products of more eomplex skeletons. Though the first report on allenic compounds involved in a MBH reaction dates back to the DABCO-catalyzed and butyllithium-promoted aldol condensation of allenic ester with aldehydes reported by Tsuboi et there are very few reports of MBH reactions involving allenoates because they easily undergo cycloaddition reactions under different Lewis bases. For instance, five-membered pyrrolidine 

MBH reaction, it was assumed that a change of mechanism involving direct formation of the anion by abstraction of the a proton had taken place when a stoichiometric amount of butyllithium was employed. 

As an analogue of allenic ester, allenic ketone 48, such as 3-methylpenta-3,4-dien-2-one and 3-benzylpenta-3,4-dien-2-one, have also been used as activated olefins for the MBH reaction. The reactivities of both allenic ketones and 

Ar = Ph, 4-MeOPh, 2-MeOPh, 4-t-BuPh, 4-BiPh, 2-naphthyl, 1-naphthyl, 4-CF3Ph, i-Pr 

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