Crotofolane-Type Diterpenoids, Crotocascarins L–Q, and a Rearranged Crotofolane-Type Diterpenoid, Neocrotocascarin, from the Stems of Croton cascarilloides

From the stems of Croton cascarilloides, further crotofolane-type diterpenoids, named crotocascarins L-Q (1-6), and a rearranged one (7), named neocrotocascarin were isolated. Their structures were elucidated from spectroscopic evidence. Also, the structures of crotocascarin O (4) and neocrotocascarin (7) were determined by X-ray crystallographic analyses. As a result, neocrotocascarin (7) was found to possess a new carbon framework. A plausible mechanism for the formation of neocrotocascarin (7) is also discussed.