ORGN 135 |
| Harriet A. Lindsay, Maria C. Milletti, Powen Hsueh, and Eun-Hoo Kim. Department of Chemistry, Eastern Michigan University, Ypsilanti, MI 48197 |
| The aza-Cope Mannich reaction sequence has been used to generate pyrrolidines and to efficiently install stereocenters on those molecules. As part of an ongoing project directed toward synthesizing natural and unnatural polyhydroxylated pyrrolizidine alkaloids, we are employing the aza-Cope Mannich reaction to install the relative stereochemistry in the B ring of Alexine (5). Because the aza-Cope reaction proceeds via a chair-like intermediate, the stereochemical outcome is, in part, dependent upon the initial iminium geometry. Theoretical calculations of iminium cations ions 2a and 2b revealed 2a to be favored by 2.7 kcal/mol. Indeed, condensation of alcohol 1 with acetaldehyde followed by aza-Cope—Mannich cyclization of the resulting iminium cation produced pyrrolizidine 4 as the major product. Details of the calculations, efforts at synthesizing the C-2 epimer of pyrrolizidine 4, and progress toward the synthesis of (+)-Alexine (5) will be described. |
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New Reactions and Methodology, Metal-Mediated Reactions, Heterocycles and Aromatics
8:00 PM-10:00 PM, Sunday, March 28, 2004 Anaheim Convention Center -- Hall A, Poster
Division of Organic Chemistry |
