Diversification of structurally significant cycloartane-type triterpenes: exploiting beddomeilactone.

The cycloartane-type triterpenes are a structurally important class of natural products with diverse biological activity. Here, we present synthetic strategies and chemical modifications for obtaining a number of recently reported cycloartane-type triterpenes, along with various close-to-natural novel derivatives. The naturally abundant beddomeilactone () serves as the key resource for most transformations. Notably, the linear sequences we put forward for synthesising three natural products from , include the selective reduction of to generate the with desired stereochemistry, the lactonization of gives qualitatively, and a selective olefin reduction of gives . Further selective olefin reduction of and was carried out in order to produce dihydro-analogues ( and ). Acid-catalyzed esterification of led to retro-aldol, forming novel analogue ; also synthesised the expected ester derivative . Subsequent transformations, such as epoxidation, lactone ring opening, and amidation, produced diverse synthetic analogues (). We also efficiently converted compound into 2,4---binectarilactone (), a structural analogue of .