Protonation lithium dienolates

The effect of base is interesting since the reaction of 458 with lithium thiopheno-late also produced a /fy-unsatu rated enone 459 [204]. In the presence of a base, anionic RS attacks the fi-C to form a dienolate intermediate, in which the Jt-bonds are orthogonal to each other. The y-protonation needs a 90° rotation of the a,/3-C-C single bond to form ,/i-unsaturated enones thus the reaction afforded a /j,y-unsaturated enone via a-protonation [193]. 

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