5.
Studies in Stereochemistry XIV. Diels-Alder adducts in the resin series; action of peracids and acid-catalysed ring opening of epoxides The synthesis of
Diels-
Alder compounds of type 2 with a 17-nor-13(14)-atisène skeleton is described (cf.
Schemes 1–3). Depending on the nature and configuration of substituents R
1 and R
2 on the carbon atoms 15 and 16, an epoxide ( 24–33 ) or a ketone ( 35–38 ) or a mixture of epoxide, ketone and lactone is obtained by the action of
p-nitroperbenzoic acid on the double bond of these adducts (cf.
Scheme 4). A simplified reaction scheme is suggested to explain the formation of the various products. In an acid-catalysed reaction, the epoxides isomerize mainly into ketones. Nevertherless, in some cases, dienes (
e.g. 52 ) or hydroxy-γ-lactones of (13
R*, 14
S*)-configuration (
e.g. 50 ) resulting from the opening of the epoxide ring with retention of configuration were obtained.
相似文献