X=y-ZH compounds as potential 1,3-dipoles. part 44. 1 Asymmetric 1,3-dipolar cycloaddition reactions of imines and chiral cyclic dipolarophiles

Article abstract of DOI:10.1016/0040-4020(95)00397-Q

Metallo 1,3-dipoles generated in situ from both aryl and aliphatic imines of α-amino esters by the action of silver salts and tertiary amines undergo cycloaddition at room temperature to 5R-(1′R, 2′S, 5′R-menthyloxyl)-2(5H)-furanone and to N-acetyl-5R-isopropoxy-2(5H)pyrrolone giving homochiral cycloadducts in good yield in all cases. π-Interaction between the dipolarophile carbonyl group and the aryl group in the aryl imines is not required for good induction. The stronger the base the faster the cycloaddition with 2-t-butyl-1,1,3,3tetramethylguanidine > DBU > NEt₃. X-Ray crystal structures of representative cycloadducts establish the absolute configuration of the pyrrolidine stereocentres.