Application of Chiral Cationic Catalysts to Several Classical Syntheses of Racemic Natural Products Transforms Them into Highly Enantioselective Pathways
摘要:
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 B-12 (Eschenmoser), (4) myrocin C (Chu-Moyer/Danishefsky), (5) coriolin and hirsutene (Mehta), (6) dendrobatid 251F (Aube), (7) silphinene (Ito), and (8) nicandrenone core (Stoltz/Corey).
Simple, Catalytic Enantioselective Syntheses of Estrone and Desogestrel
作者:Qi-Ying Hu、Pankaj D. Rege、E. J. Corey
DOI:10.1021/ja048808x
日期:2004.5.1
Highly enantioselective and very shortsyntheses of the bioactive forms of estrone (3) and desogestrel (4) are described using a chiral oxazaborolidinium catalyst (2) in the key initial step. Enantiomerically pure estrone was synthesized in eight steps from the readily available starting materials diene 5 and alpha,beta-enal 6 viaintermediates 8 and 9. Desogestrel was synthesized using a similar strategy