Diastereoselective cycloaddition of N-lithiated azomethine ylides to (E)-.alpha.,.beta.-unsaturated esters bearing a C2-symmetric 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.
Synthesis of chiral azamacrocycles using the bis(α-chloroacetamide)s derived from chiral 1,2-diphenylethylenediamine
作者:Kejiang Hu、Jerald S. Bradshaw、N. Kent Dalley、Guoping Xue、Reed M. Izatt、Krzysztof E. Krakowiak
DOI:10.1002/jhet.5570360204
日期:1999.3
secondary diamines with the (R,R)- and (S,S)- forms of 1,2-bis(N-methyl-α-chloracetamido)-1,2-diphenylethane (20). Macrocyclic diamides 9 and 10 were reduced to form the optically active diphenyl-substituted hexaaza-18-crown-6 (13) and tetraaza-12-crown-4 (14), respectively. Reduction of macrocyclic diamide ligands 11 and 12 gave a complex mixture of products from which the desired tetraaza-15-crown-5