Application of Cp2TiCl-Promoted Radical Cyclization: A Unified Strategy for the Syntheses of Iridoid Monoterpenes.

An expedient approach toward the unified total syntheses of (+)-iridomyrmecin, (-)-isoiridomyrmecin, (+)-7- epi-boschnialactone, (+)-teucriumlactone, and (-)-dolichodial in chirally pure forms starting from readily available (+)-β-citronellene is delineated combining step economy and simplicity. Highlights include a Ti(III)-mediated reductive epoxide opening-cyclization for the construction of the core cyclopenta[ c]pyran skeleton of the iridoid lactones with complete diastereoselectivity for the newly created bridgehead stereogenic centers. Subsequent transformations facilitate a short access to (+)-teucriumlactone and (-)-dolichodial and formal access to potentially other iridoids.