title: Divergent Stereocontrolled Synthesis of the Enantiopure Tetracyclic Cores of Asparagamine A and Stemofoline via an Intramolecular 2-Propylidine-1,3-(bis)silane Bicyclization.
abstract: A concise and highly diastereoselective synthesis of the polyfused tetracyclic cores of the Stemona alkaloids asparagamine A and stemofoline that relies on a 2-propylidine-1,3-(bis)silane bicyclization onto a enantiodefined pyrrolidine 2,5-di(cation) equivalent derived from l-malic acid is reported. A crucial feature of this divergent synthetic approach involves the solvolysis of a transient and highly labile tertiary-propargylic hydroxylactam trifluoroacetate in the strongly ionizing medium 5 M LiClO4/Et2O. The acyliminium ion generated in this manner undergoes stereospecific interception by the aforementioned (bis)silane nucleophile.
authors.affiliation: Department of Chemistry and Biochemistry, Montana State University , Bozeman, Montana 59717, United States.
authors.forename: Bryon K
authors.initials: BK
authors.lastname: Anderson
authors.affiliation: Department of Chemistry and Biochemistry, Montana State University , Bozeman, Montana 59717, United States.
authors.forename: Tom
authors.initials: T
authors.lastname: Livinghouse
mesh_terms: D018360:Crystallography, X-Ray; D003500:Cyclization; D006576:Heterocyclic Compounds, 4 or More Rings / Q000138:chemical synthesis* / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D013237:Stereoisomerism; D014297:Trimethylsilyl Compounds / Q000737:chemistry*
chemical_list: D006576:Heterocyclic Compounds, 4 or More Rings; D014297:Trimethylsilyl Compounds; C481859:didehydrostemofoline; C430220:stemofoline