DIASTEREOSELECTIVE CYCLOADDITION OF N-LITHIATED AZOMETHINE YLIDES TO (E)-ALPHA,BETA-UNSATURATED ESTERS BEARING A C2-SYMMETRICAL IMIDAZOLIDINE CHIRAL CONTROLLER

The 1,3-dipolar cycloaddition of N-metalated azomethine ylides to chiral (E)-3-(1,3-disubstituted 4,5-diphenylimidazolidin-2-yl)propenoates proceeded highly diastereoselectively. The previously unknown absolute configuration of optically pure 1,2-dianilino-1,2-diphenylethane was determined from the absolute configuration of the cycloadducts. What diastereotopic olefin face of the alpha,beta-unsaturated ester was attacked by the ylide was found to depend dramatically upon the nature of N substituents of the chiral controller as well as upon the bulkiness of the ester moiety of the ylide.