1,3-Dipolar cycloadditions of azomethine ylides with chiral acrylates derived from methyl (S)- and (R)-lactate: diastereo- and enantioselective synthesis of polysubstituted prolines
                                
                                    
                                        作者:Carmen Nájera、M. de Gracia Retamosa、José M. Sansano                                    
                                    
                                        DOI:10.1016/j.tetasy.2006.07.006
                                    
                                    
                                        日期:2006.8
                                    
                                    The 1,3-dipolar cycloaddition of acrylates derived from methyl (R)- and (S)-lactate, as chiral dipolarophiles, with glycine and alanine derived azomethine ylides is described for the first time. By using the corresponding silver metallo-azomethine ylides polysubstituted endo-prolines were obtained with high diastereo- and enantioselectivity. The process occurs at room temperature in toluene with 10 mol % of AgOAc by using either KOH or Et3N as bases, also in substoichiometric amounts. Under these mild reaction conditions, enantiomerically enriched polysubstituted prolines resulting from an endo approach were obtained in general in high yields and de (86-99%). The absolute configuration of the resulting prolinates can be determined on the basis of X-ray diffraction analysis. (c) 2006 Elsevier Ltd. All rights reserved.