An NMR Strategy for Determination of Configuration of Remote Stereogenic Centers:  3-Methylcarboxylic Acids
                                
                                    
                                        作者:Thomas R. Hoye、Dmitry O. Koltun                                    
                                    
                                        DOI:10.1021/ja972664n
                                    
                                    
                                        日期:1998.5.1
                                    
                                    A method has been developed for determining the absolute configuration of carboxylic acids bearing a methyl substituent at C(3). A series of 1-arylethylamide derivatives of such acids was prepared in which both the amine- and acid-derived portions were of known configuration. Diagnostic chemical shift differences (Delta delta's) were identified for various proton resonances in each pair of diastereomeric amides and a new method was established based on the observed trends. A conformational model (supported by computational calculations) consistent with the observed differential shielding effects is offered. This approach represents a general strategy that can be adapted to other substructures.