Proof of the structure of the Stemodia chilensis tetracyclic diterpenoid (+)-19-acetoxystemodan-12-ol by synthesis from (+)-podocarpic acid. X‑ray structure determination of a key intermediate

The first synthesis of (+)-19-acetoxystemodan-12-ol (1), a stemodane diterpenoid isolated from Stemodia chilensis, is described. The structure was supported by an X-ray crystallographic analysis of intermediate (+)-9a, which confirmed the proposed structure and excluded the structure of (−)-19-hydroxystemod-12-ene as a possible candidate for the Chilean Calceolaria diterpenoid to which the (−)-19-hydroxystemar-13-ene structure (9b) had been erroneously assigned