The first semisynthetic routes toward terrestrial anti-inflammatory natural products linariophyllene A-C and the refined route toward marine natural product rumphellolide H are presented. Among the synthesized target compounds, the correct structure of linariophyllene A was determined to be the diastereomer of the originally proposed structure with an inverted stereocenter at the secondary alcohol. The proposed structures of linariophyllene B and rumphellolide H were confirmed. However, the correct structure of linariophyllene C was found to be the diastereomer of the originally proposed structure with an inverted stereocenter at the tertiary carbon of the epoxide moiety. The structures of linariophyllenes A-C and rumphellolide H were unequivocally confirmed by single-crystal X-ray diffractometry. The obtained results enabled the proposal of the biosynthetic origins of the aforementioned natural products and bolstered the diversity of available sesquiterpenoids. Linariophyllenes A-C and rumphellolide H were obtained in sufficient amounts to further expand their bioactivity profile and utility as reference standards in future studies of chemical constituents of terrestrial and marine organisms.