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Tuesday, August 25 • 2:00pm - 2:40pm
[0046] A Divergent Stereocontrolled Synthesis of the Enantiopure Tetracyclic Cores of Asparagamine A and Stemofoline via an Intramolecular 2-Propylidine-1,3-(bis)silane Bicyclization

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A concise and highly diastereoselective synthesis of the polyfused tetracyclic cores of the Stemoa 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 will be described.  A crucial feature of this divergent synthetic approach involves the solvolysis of a transient and highly labile tertiary-propargylic lactamol trifluoroacetate in the strongly ionizing medium 5M LiClO4/Et2O. The acyliminium ion generated in this manner undergoes stereospecific interception by the aforementioned (bis)silane nucleophile (Scheme 1).

The second topic of this discussion will be concerned with highly diastereoselective metalloamination/cyclizations of zinc(II) hydrazides derived from the reaction of diethylzinc and N,N-dimethylhydrazinoalkenes. The resulting organozinc intermediates have been found to undergo facile allylation and acylation, in-situ, to provide the corresponding functionalized piperidines and pyrrolidines respectively (Scheme 2).

Invited Lecturers
avatar for Thomas Livinghouse

Thomas Livinghouse

Professor of Chemistry, Montana State University
B.S., University of California, Los Angeles, 1976; M.S., University of California, Los Angeles, 1977; Ph.D., Rice University, 1980; Postdoctoral, Stanford University, 1981.Awards and Professional Activities:Departmental Scholar (Chemistry), 1974 - 1976 University of California, Los... Read More →

Tuesday August 25, 2015 2:00pm - 2:40pm PDT
Corwin East