FUNCTIONALIZATION REACTIONS OF A MEDIUM-RING BRIDGEHEAD ENONE THAT SKIRT TRANSANNULAR BOND FORMATION

As a consequence of the close proximity of the olefinic and carbonyl centers in ketone 4, the molecule participates readily in transannular reactions. Sequences have been developed for enhancing the level of functionality in both of these sectors within the central medium-sized ring without incurring ring closure. Osmate ester 10 is especially serviceable, permitting direct access to triol 11 and to the olefinic hydroxy acetate 17. In a companion study, acetals 19a and 19b were prepared from 11 and dehydrated with the Burgess reagent. The trans cycloalkene generated in each instance was shown to possess the topography found in 21, a conclusion that was further supported by deuterium labeling experiments. Access to this diastereomer made possible the acquisition of diacetates 23a and 23b, where seven of the nine carbon atoms of the central ring are stereogenic and have well-defined absolute stereochemistry.