Application of Chiral Cationic Catalysts to Several Classical Syntheses of Racemic Natural Products Transforms Them into Highly Enantioselective Pathways
- 1 October 2004
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 126 (42), 13708-13713
- https://doi.org/10.1021/ja046154m
Abstract
This paper describes the application of chiral oxazaborolidinium cations of type 2 to various enantioselective Diels−Alder reactions that have served as early key steps for the syntheses of complex natural products. In the original syntheses these Diels−Alder reactions produced racemic adducts and led to racemic target molecules unless a separation of enantiomers by classical resolution was employed. By use of chiral catalysts of type 2, chiral products were obtained directly from Diels−Alder reactions of achiral components in excellent yield and enantioselectivity and with the mechanistically predicted absolute configuration. As a result, a number of classical syntheses could be converted to enantioselective versions, including (1) cortisone/cortisol (Merck/Sarett), (2) dendrobine (Kende), (3) vitamin B12 (Eschenmoser), (4) myrocin C (Chu-Moyer/Danishefsky), (5) coriolin and hirsutene (Mehta), (6) dendrobatid 251F (Aubé), (7) silphinene (Ito), and (8) nicandrenone core (Stoltz/Corey).Keywords
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