Exploratory studies aimed at a synthesis of vinigrol. 3. Evaluation of a lactone bridge as a conformational lock

Evaluated in the present investigation are possible synthetic approaches to vinigrol based on the involvement of lactone rings as tools for the conformational rigidification of functionalized cis-octalins. Emphasis was placed on the structural arrangements resident in 3 and 5. The first of these systems proved to be highly strained and inaccessible. Especially notable was the finding that hydroxy ketenes 14 and 21 could be isolated and shown not to be amenable to cyclization when heated. The stereo-controlled assembly of 5 was successfully accomplished through exploitation of a related synthetic pathway. However, neither this attractive intermediate nor its close relative 33 could be processed in a manner that delivered the vinigrol framework. Nonetheless, several features of the routes deployed offer the prospect of wider application in other contexts.