Methods for a stereoselective preparation of compounds of type 2b, a key intermediate of a previous synthesis of the tetracyclic diterpene stemarin (1a), have been tested on model compounds 5a, 5c, and 8a. Thus, (+/-)-(1RS,6SR,8SR,11RS)-11-hydroxytricyclo[184.108.40.206(1,6)]dodecan-9-one (5a) was transformed by the Mitsunobu reaction into (+/-)-(1RS,6SR,8SR,11SR)-11-(benzoyloxy)tricyclo[220.127.116.11(1,6)]dodecan-9- one (6b; Scheme 2). The latter was also obtained from (+/-)-(1RS,6SR,8SR,11RS)-11-[(4-toluenesulfonyloxy]tricyclo[18.104.22.168(1,6) ]dodecan-9-one (5c) by the action of Et4N (PhCOO) in acetone. Compound 6b was then converted into (+/-)-(1RS,6RS,8RS,9RS)-tricyclo[22.214.171.124(1,6)]dodecan-9-ol (8b), a model for 2b. Compound 8b was also prepared from its epimer 8a by the Mitsunobu reaction via ester 7b. The inversion of configuration of bicyclo[2.2.2]octan-2-ols or derivates was not previously described. The model studies paved the way to the diastereoselective synthesis of (+)-18-deoxystemarin (1b) via 12-beta-hydroxy-13-methyl-9-beta,13-beta-ethano-9-beta-podocarpan-15-one (10a) and 13-methyl-9-beta,13-beta-ethano-9-beta-podocarpan-12-alpha-ol (11b).
|Titolo:||STUDIES FOR A DIASTEREOSELECTIVE SYNTHESIS OF THE TETRACYCLIC DITERPENIC DIOL STEMARIN - A MODEL STUDY FOR A NEW PREPARATION OF THE KEY INTERMEDIATE AND THE SYNTHESIS OF (+)-18-DEOXYSTEMARIN|
ROMEO, SERGIO (Ultimo)
|Settore Scientifico Disciplinare:||Settore CHIM/08 - Chimica Farmaceutica|
|Data di pubblicazione:||1991|
|Digital Object Identifier (DOI):||10.1002/hlca.19910740807|
|Appare nelle tipologie:||01 - Articolo su periodico|