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

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[6.2.2.0(1,6)]dodecan-9-one (5a) was transformed by the Mitsunobu reaction into (+/-)-(1RS,6SR,8SR,11SR)-11-(benzoyloxy)tricyclo[6.2.2.0(1,6)]dodecan-9- one (6b; Scheme 2). The latter was also obtained from (+/-)-(1RS,6SR,8SR,11RS)-11-[(4-toluenesulfonyloxy]tricyclo[6.2.2.0(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[6.2.2.0(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)

UNPRECEDENTED OUTCOME OF THE ALLENE PHOTOADDITION TO A FUSED ALPHA,BETA-UNSATURATED KETONE

The unprecedented formation, in the course of the allene photoaddition to 18-benzyloxy-8(9)-podocarpen-14-one, of a by-product, due to a novel type of intramolecular hydrogen abstraction by the biradical intermediate, is described

STUDIES FOR A DIASTEREOSELECTIVE SYNTHESIS OF THE TETRACYCLIC DITERPENIC DIOL STEMARIN - AN IMPROVED PROCEDURE FOR THE SYNTHESIS OF 8(9)-PODOCARPEN-14-ONES - THE TOTAL SYNTHESIS OF 18-BENZYLOXY-8(9)-PODOCARPEN-14-ONE AND RELATED STUDIES

An efficient preparation of 18-benzyloxy-8(9)-podocarpen-14-one, 3a, a key intermediate for a diastereoselective synthesis of the bicyclo[2.2.2]octan-2-ol, 1, precursor of the tetracyclic diol stemarin, 2, is described. The approach outlined can be, in principle, applied to the preparation of related compounds