✍ Scribed by Luis R. Domingo; M. Teresa Picher; Juan Andrés
No coin nor oath required. For personal study only.
The molecular mechanism of the domino reaction of nitroalkenes with silyl enol ethers to give nitroso acetal adducts was characterized using computational procedures at the PM3 semiempirical level. The domino process comprises three consecutive steps: the first and rate-determining step is the nucleophilic attack of the silyl enol ether on the nitroalkene to give a zwitterionic intermediate; closure of this intermediate leads to a nitronate intermediate, which then affords the final nitroso acetal adduct through an intramolecular [3 2] cycloaddition. The presence of both silicon and oxygen atoms in the silyl enol ether increases the nucleophilic character of the carboncarbon double bond and favors the ionic character of the first step. The presence of the Lewis acid promotes the delocalization of the negative charge transferred in the nucleophilic attack of the silyl enol ether to the nitroalkene and decreases the activation energy of the rate-determining step. The inclusion of solvent effects predicts a stabilization of the first zwitterionic intermediate and therefore emphasizes the stepwise mechanism for the first cycloaddition of this domino reaction.
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