Synthesis of 3,4‐Dihydro‐2
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‐Pyrroles from Ketones, Aldehydes, and Nitro Alkanes via Hydrogenative Cyclization
作者:Barbara Klausfelder、Patricia Blach、Niels de Jonge、Rhett Kempe
DOI:10.1002/chem.202201307
日期:2022.8.22
developed and employed for the synthesis of 3,4-dihydro-2H-pyrroles via hydrogenation and subsequent cyclization of nitro ketones. The catalyst was identified from a library of 24 heterogeneous catalysts. The key to our hydrogenation/cyclization reaction is the tolerance of aldehydes and ketones as functional groups and the ability to hydrogenate aliphaticnitrocompounds efficiently.
Silylation of gamma-nitro ketones of the general formula (RCOCH)-C-1(R-2)CH(R-3)CH(R-4)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 R-1 = Ar or cyclo-C3H5. Enoximes are generated as the silylation products of the starting ketones with enhanced P-proton mobility (R-3 CO2Me or 4-NO2C6H4). The presence of an alkyl group at the carbonyl function (R-1 = Alk) is favorable for the formation of enoximes. Finally, the introduction of a substituent at the a position with respect to the nitro group (R-4 = 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.
THE ACTION OF HEAT ON CERTAIN BROMONITRO COMPOUNDS