A Chemical Study of Burley Tobacco Flavour ( Nicotiana tabacum L.) VII. Identification and synthesis of twelve irregular terpenoids, related to solanone, including 7,8‐dioxabicyclo[3.2.1]octane and 4,9‐dioxabicyclo[3.3.1]nonane derivatives

Twelve novel constituents isolated from Burley tobacco condensate by semi‐preparative GLC. have been identified as ( E )‐3,4‐epoxy‐5‐isopropyl‐nonane‐2,8‐dione ( A ), exo ‐(1‐methyl‐4‐isopropyl‐7,8‐dioxabicyclo[3.2.1]oct‐6‐yl)methyl ketone ( B ), exo ‐1‐(1‐methyl‐4‐isopropyl‐7,8‐dioxabicyclo[3.2.1]oct‐6‐yl)‐ethanol ( C ), ( E )‐5‐isopropyl‐8‐hydroxy‐8‐methyl‐non‐6‐en‐2‐one ( D ), ( E )‐5‐isopropyl‐6,7‐epoxy‐8‐hydroxy‐8‐methyl‐nonan‐2‐one ( E ), endo ‐2‐(1‐methyl‐4‐isopropyl‐7,8‐dioxabicyclo[3.2.1]oct‐6‐yl)‐propan‐2‐ol ( F ), 3,3,5‐trimethyl‐8‐isopropyl‐4,9‐dioxabicyclo[3.3.1]nonan‐2‐ol ( G ), (E)‐5‐isopropyl‐non‐3‐ene‐2,8‐diol ( H ), 5‐isopropyl‐nonane‐2,8‐diol ( I ), (E)‐5‐isopropyl‐8‐hydroxy‐non‐6‐en‐2‐one ( J ), 5‐isopropyl‐8‐hydroxy‐nonan‐2‐one ( K ), and (E)‐3‐isopropyl‐6‐methyl‐hepta‐4,6‐dien‐1‐ol ( L ). Compounds A–K were synthesized from norsolanadione ( 2 ), and compound L from 2‐isopropyl‐5‐oxo‐hexanal ( 15 ). The relative configuration of the bicyclic internal acetals B, C, F, G and their δ‐keto‐epoxide precursors A and E is discussed. All these Burley tobacco flavour components belong to a growing family of metabolites structurally related to solanone ( 1 ). They are believed to arise from the breakdown of cembrene‐type precursors.