Polar aprotic solvents, enol stability

While the addition/oxidation and the addition/protonation procedures are successful with ester enolates as well as more reactive carbon nucleophiles, the addition/acylation procedure requires more reactive anions and the addition of a polar aprotic solvent (HMPA has been used) to disfavor reversal of anion addition. Under these conditions, cyano-stabilized anions and ester enolates fail (simple alkylation of the carbanion), but cyanohydrin acetal anions are successful. The addition of a cyanohydrin acetal anion to l,4-dimethoxynaphthalene-Cr(CO)3 occnrs by kinetic control at C-/3 in THF/HMPA and leads to the O -diacetyl derivative after methyl iodide addition and hydrolysis of the cyanohydrin acetal. Monoacylation of 1,4-dimethoxynaphthalene-Cr(CO)3 has been achieved nsing the seqnence of reactions shown in eqnation (126). ... 

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