In summary, we established an atypical polyene cyclization strategy that converts easily accessible b-ionyl derivatives into polycyclic [4.4.1]-propellanes. Unlike canonical biomimetic Scheme 5. Entry to diversified non-natural abeo-abietanes via skeletal remodeling of propellanes 10 and 11. polyene cyclization, this strategy allows for complete control of regiochemistry and tolerates a range of electron-rich and electron-deficient (hetero)aryl groups. The strained polycycles produced from this chemistry were elaborated to diterpene architectures via late-stage skeletal remodeling. This powerful feature was highlighted in a unified synthesis of taxodione (8) and salviasperanol (9) that is concise, modular, and amenable to asymmetric induction in future iterations. Alternative diversification pathways were explored, and these generated a collection of non-canonical abeo-abietane scaffolds that would be difficult or impossible to prepare using conventional biomimetic logic. As a result, this terpene assembly strategy appears to be well-suited for applications in both target-and diversityoriented synthesis.