Magnesium Methyl Carbonate-Activated Alkylation of Methyl Ketones with an ω-Halo Nitrile, Esters, and Amides
作者:Elli S. Hand、Stephen C. Johnson、David C. Baker
DOI:10.1021/jo960330v
日期:1997.3.1
Terminally substituted, extended-chain derivatives of the 2-dibenzofuranyl methyl ketone 6 and its phenylethyl analogue 12 were readily obtained by converting the ketones to magnesium chelates of their beta-carboxylated enolates with magnesium methyl carbonate (MMC, methyl methoxymagnesium carbonate, Stiles's reagent), followed by alkylation in situ with omega-halo compounds, X(CH2)(n)Y where X = Br and Y = CO(2)Me, CN, CONMe(2), CON(i-Pr)(2), CON(CH2)(4), or CON(CH2)(5) for n = 1; X = Br or I, and Y = CO(2)Me for n = 2; and X = Br and Y = CO(2)Me for n = 3. Dimethylcarbamoyl chloride (n = 0) gave products derived from MMC and the solvent, N,N-dimethylformamide. The order of reactivity of the halides was alpha > beta > gamma and beta-I > beta-Br. beta-Bromo amides were found to be unsuitable reactants. Lower reaction temperatures favored alkylation over competing elimination of HX from methyl beta-halopropionate. No self-condensation products of the ketones were observed; however, bis-alkylation and monomethylation products were formed when reaction times were prolonged. In contrast to the unsubstituted beta-keto acid 13, all intermediate alpha-alkyl beta-keto acids decarboxylated during the reaction or the workup.