Use of the nonionic superbase P(MeNCH2CH2)3N in the selective monoalkylation of active-methylene compounds

The symmetric active-methylene compounds CH2(CO2Et)(2) and CH2[C(O)Me](2) are selectively monoalkylated in the presence of 1.1 equiv of a variety of alkyl halides and 1 equiv of the nonionic superbase P(MeNCH2CH2)(3)N in 85-98% yields in 30 min at room temperature. The unsymmetrical active-methylene compound EtO2CCH2C(O)Me is selectively monoalkylated under the same conditions, except for the temperature, which is 0 degrees C, in 59-88% yields. The observation of selective C-rather than O-alkylation is rationalized in terms of the formation of an enolate whose negatively charged oxygen is sterically protected by a nearby HP(MeNCH2CH2)(3)N+ counterion in a tight ion pair.