Highly Stereoselective trans Addition of π-Type Nucleophiles to a Bicyclic N-Acyliminium Ion – Application to the Synthesis of Indolizidine and Pyrrolizidine Alkaloids

✍ Scribed by Hamid Dhimane; Corinne Vanucci-Bacqué; Louis Hamon; Gérard Lhommet

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 446 KB
• Volume: 1998
• Category: Article
• ISSN: 1434-193X
• DOI: 10.1002/(sici)1099-0690(199809)1998:9<1955::aid-ejoc1955>3.0.co;2-u

✦ Synopsis

Enantiopure bicyclic 5-ethoxytetrahydropyrrolo[1,2-c]oxa-disubstituted pyrrolidines was illustrated by formal syntheses of 3,5-disubstituted indolizidine toxins, starting from 5-zol-3-one 1b was prepared in two steps from the known tosylate 4, which is readily available from (S)-pyroglutamic allyltetrahydropyrrolo[1,2-c]oxazol-3-one 2a. Moreover, an enantiodivergent synthesis of the pyrrolizidine alkaloids (+) acid. Trapping of the N-acyliminium ion (I), generated in situ from 1b in the presence of Lewis acid, with various silylated and (-)-xenovenine was achieved starting from the same chiral building block 2a. π-type nucleophiles gave rise selectively to trans adducts 2. The usefulness of this stereoselective access to trans-2,5-