Triethyloxonium tetrafluoroborate regioselectivity

Alkylation of enolate anions usually gives C-alkylation and is therefore not suitable for the preparation of enol ethers. The exception is when triethyloxonium tetrafluoroborate is used as the alkylating agent in a dipolar aprotic solvent.11 O-Alkylation can be regioselectively achieved if the enolate anion is derived from acetoacetate or a similar compound. On the other hand, O-acylation of enols or enolate anions is quite common. Enol esters can therefore be prepared readily from the parent carbonyl compounds. For... 

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