Electrophilic and Nucleophilic Reactivities of the Azomethine Carbon of SAMP-Hydrazones: Stereoselective Synthesis of γ-Amino Ketone Derivatives
作者:Dieter Enders、Elena Díez、Rosario Fernández、Eloísa Martín-Zamora、Jesús M. Muñoz、Rafael R. Pappalardo、José M. Lassaletta
DOI:10.1021/jo990503r
日期:1999.8.1
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.