Novel and Stereocontrolled Synthesis of Enantiopure and Polyalkyl Substituted Piperidines
作者:Christoph Schneider、Christoph Börner
DOI:10.1055/s-1998-1725
日期:1998.6
A flexible and stereodivergent synthesis of enantiopure piperidines with up to four alkyl-substituted chiral centers is reported which proceeds by way of a double nucleophilic addition of primary amines to the 7-oxo-2-enimides 1. These in turn are accessible via the silyloxy-Cope rearrangement of chiral syn-aldol products.
of our synthesis is a silyloxy-Coperearrangement of the chiral, silylated aldol product 2 which proceeds selectively through the chair-like transition state with the silyloxy group in the pseudoaxial and the carboximide group in the pseudoequatorial position. The two methyl-substituted stereogenic centers of the natural product are generated with ds > 97:3. The rearrangement product 4 is converted
oxa-conjugate addition has been employed in a stereoselective synthesis of enantiopure polyalkyl-substituted tetrahydropyrans, which are frequently found as substructures in many natural products. The requisite cyclization precursors, 7-hydroxy-2-enimides 3 and 7-hydroxy-2-enoates 6 were easily accessible by silyloxyCoperearrangements of the appropriate chiral syn-aldols. It was found that the stereoselectivity
Enantiopure piperidines 4 may be accessed in very good overall yields and high stereoselectivity from the bifunctional products 2 of the silyloxyCoperearrangement of chiralaldolproducts 1 by sequential nucleophilic addition of primary amines and subsequent hydrogenation. The reaction is proposed to proceed by initial imine formation followed by an intramolecular aza-conjugate addition to the α
Stereodivergent Synthesis of Enantiopure Tetrahydropyrans via the Silyloxy-Cope Rearrangement of Chiral Aldol Products
作者:Christoph Schneider
DOI:10.1055/s-1997-5748
日期:1997.7
A stereoselective synthesis of highly substituted and enantiopure tetrahydropyrans from chiral 7-hydroxy-2-alkenoic imides and esters is described. Depending on the carboxylic acid derivative the base-induced cyclization is kinetically or thermodynamically controlled to deliver either tetrahydropyran stereoisomer selectively.