Silylation of γ-nitro ketones as a convenient approach to the synthesis of 2-[N,N-bis(silyloxy)amino]-2,3-dihydrofurans and conjugated enoximes

Silylation of γ-nitro ketones of the general formula R1COCH(R2)CH(R3)CH(R4)NO2 proceeded stereoselectively to give 2-[N,N-bis(trimethylsilyloxy)amino]-2,3-dihydrofurans, conjugated enoximes, silylation products of the carbonyl group or both functional groups, or N,N-bis(trimethylsilyloxy)enamine depending on the nature and positions of the substituents in the carbon skeleton. Dihydrofuran derivatives are formed for R1 = Ar or cyclo-C3H5. Enoximes are generated as the silylation products of the starting ketones with enhanced β-proton mobility (R3 = CO2Me or 4-NO2C6H4). The presence of an alkyl group at the carbonyl function (R1 = Alk) is favorable for the formation of enoximes. Finally, the introduction of a substituent at the α position with respect to the nitro group (R4 = Me, CO2Me, or Ph) leads to the formation of silyl enolates. Under the action of NH4F in MeOH, dihydrofurans can be transformed into substituted furans in moderate yields.