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26.1.9.3 Method 3: Monoalkylation of Potassium Enolates

DOI: 10.1055/sos-SD-026-00361

Plaquevent, J.-C.; Cahard, D.; Guillen, F.Science of Synthesis, (200526473.

As is the case with sodium enolates, kinetic deprotonation of ketones is observed when potassium hexamethyldisilazanide is used as the base in tetrahydrofuran at low temperature.[‌9‌] However, most of the reported reactions involving potassium ketone enolates proceed under equilibrating conditions with potassium hydride or potassium alkoxide bases. Some typical examples are given in Table 5.[‌41‌‌43‌] One can observe that potassium enolates are employed especially when the starting ketone is to be polysubstituted, since potassium enolates are easily polyalkylated (see Section 26.1.9.11).

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The monoalkylation of potassium enolates with memory of chirality is a fascinating concept which implies that a nonracemic chiral compound can be alkylated without the aid of an external chiral source and still retain chirality. Whilst most of the reported examples of this type of reaction are in the field of amino acid chemistry,[‌45‌] one of the first significant examples was observed in the chemistry of ketone alkylations.[‌46‌] An excellent review has surveyed this topic.[‌47‌]

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