Electrophilic and Nucleophilic Reactivities of the Azomethine Carbon of SAMP-Hydrazones: Stereoselective Synthesis of γ-Amino Ketone Derivatives
摘要:
A novel methodology for the asymmetric synthesis of secondary N-Boc-protected gamma-amino ketones is described. After the highly diastereoselective nucleophilic 1,4-addition of formaldehyde SAMP-hydrazone 1 to prochiral conjugated enones 2, the carbonyl group of the resulting li-oxo aldehyde SAMP-hydrazones 4 was protected as ethylene ketals 5. The stereoselective (de 58-88%) addition of organometallic reagents to the CN double bond of the latter was then performed, and the unstable intermediate hydrazines obtained were either trapped as Moc-protected hydrazines 8 in good yields (65-87%) or reduced by Raney nickel-catalyzed hydrogenolysis of the N-N bond to afford the corresponding amines, which were isolated as their corresponding N-Boc derivatives 11. Noteworthy, the azomethine carbon of SAMP-hydrazones, not being essentially modified during the process, sequentially serves as a nucleophilic and an electrophilic center, acting as a nexus between the conjugated enone (electrophile) and the organometallic reagent (nucleophile) and helping in the creation of two adjacent stereogenic centers.
Electrophilic and Nucleophilic Reactivities of the Azomethine Carbon of SAMP-Hydrazones: Stereoselective Synthesis of γ-Amino Ketone Derivatives
摘要:
A novel methodology for the asymmetric synthesis of secondary N-Boc-protected gamma-amino ketones is described. After the highly diastereoselective nucleophilic 1,4-addition of formaldehyde SAMP-hydrazone 1 to prochiral conjugated enones 2, the carbonyl group of the resulting li-oxo aldehyde SAMP-hydrazones 4 was protected as ethylene ketals 5. The stereoselective (de 58-88%) addition of organometallic reagents to the CN double bond of the latter was then performed, and the unstable intermediate hydrazines obtained were either trapped as Moc-protected hydrazines 8 in good yields (65-87%) or reduced by Raney nickel-catalyzed hydrogenolysis of the N-N bond to afford the corresponding amines, which were isolated as their corresponding N-Boc derivatives 11. Noteworthy, the azomethine carbon of SAMP-hydrazones, not being essentially modified during the process, sequentially serves as a nucleophilic and an electrophilic center, acting as a nexus between the conjugated enone (electrophile) and the organometallic reagent (nucleophile) and helping in the creation of two adjacent stereogenic centers.