[Fireredburn1]

How would nucleophiles react with alkynones compared to enones? If we draw the resonance structure of enones, there is a positive charge on the carbon, thus attracting nucleophiles there. What about the case of an alkynone? If I were to draw the resonance for that, there is also a positive charge on the carbon, but in this case the carbon here is sp hybridised. Won't having a positive charge on a sp carbon have a destabilising effect, rendering the second resonance formed on the alkynone to be a lesser contributor? Would I expect a nucleophile to add faster on the enone?



For this question, would it be valid to guess that EA added more readily on alkynes then on alkenes because Hg2+ ion had a stronger interaction with the greater electron density on the triple bond?

[phth]

The alkyne looks like a d orbital moreso than an alkene because of the orthogonal shape of the two π orbitals.  This means that the soft lewis acid will have a stronger interaction with it.  In other words, it is a better ligand.  The alkyne can then undego a metathesis reaction forming a cylopropyl metalocycle, and then it Hg gets reduced by Nucleophilic attack. In addition, the transition state requires less energy to make, and less energy to collapse.  Once the Hg(0) species is formed, it will act like a grignard reagent, and become protonated due to the acidic conditions regenerating the catalyst Hg(II).