摘要:
The enolization of beta-amino carboxamides by lithium hexamethyldisilazide (LiHMDS) in THF/ toluene and subsequent diastereoselective alkylation with CH3I are reported. In situ IR spectroscopic studies reveal that P-amino carboxamides coordinate to LiHMDS at -78 degrees C before enolization. Comparison with structurally similar carboxamides suggests that the P-amino group promotes the enolization. I R spectroscopic studies also show that the enolization is reversible. Efficient trapping of the enolate by CH3I affords full conversion to products. Li-6 and N-15 NMR spectroscopic studies reveal that lithium enolate-LiHMDS mixed dimers and trimers as well as a homoaggregated enolate are formed during the reaction. At ambient temperature, racemization of the beta-position through a putative reversible Michael addition was observed.