188015-47-6Relevant articles and documents
Highly stereoselective trans addition of π-type nucleophiles to a bicyclic N-acyliminium ion - Application to the synthesis of indolizidine and pyrrolizidine alkaloids
Dhimane, Hamid,Vanucci-Bacque, Corinne,Hamon, Louis,Lhommet, Gerard
, p. 1955 - 1963 (1998)
Enantiopure bicyclic 5-ethoxytetrahydropyrrolo[1,2-c]oxazol-3-one 1b was prepared in two steps from the known tosylate 4, which is readily available from (S)-pyroglutamic acid. Trapping of the N-acyliminium ion (I), generated in situ from 1b in the presence of Lewis acid, with various silylated π-type nucleophiles gave rise selectively to trans adducts 2. The usefulness of this stereoselective access to trans-2,5-disubstituted pyrrolidines was illustrated by formal syntheses of 3,5-disubstituted indolizidine toxins, starting from 5-allyltetrahydropyrrolo[1,2-c]oxazol-3-one 2a. Moreover, an enantiodivergent synthesis of the pyrrolizidine alkaloids (+) and (-)-xenovenine was achieved starting from the same chiral building block 2a.