Synthesis of dihydrotropone derivatives using an anionic 8π-electrocyclic reaction.

A new method to synthesise functionalised cycloheptatrienes was established using the anionic 8π-electrocyclic reaction of ß-ketoester-derived dienyne substrates. The cyclised products were converted to a variety of cycloheptatriene derivatives including tropones. Using this method, a concise, first total synthesis of (-)-orobanone, a natural sesquiterpenoid, was achieved.

Total Synthesis and Structural Revision of the 6,11-Epoxyisodaucane Natural Sesquiterpene Using an Anionic 8π Electrocyclic Reaction.

A new synthetic strategy that forms a seven-membered carbocycle using an anionic 8π electrocyclic reaction facilitated the first total synthesis of the 6,11-epoxyisodaucane natural sesquiterpene in 9.0% yield over 10 steps in the longest linear sequence. The misassigned proposed stereochemistry was corrected by the synthesis of both the proposed structure and its C6 epimer. In addition, the 5-7-fused ring system was concisely constructed by tandem decyanation/five-membered-ring formation from an epoxynitrile.

8π Electrocyclic Reaction of Phosphonate Derivatives: Access to Seven-Membered Cross-Conjugated Cyclic Trienes.

An anionic 8π electrocyclic reaction of 4-(diethoxyphosphoryl)-1,3,6-heptatriene derivatives was developed. Under the influence of a base, the substrate underwent deprotonation at the C5 position followed by the 8π electrocyclization of the resulting heptatrienyl anion. The subsequent Horner-Wadsworth-Emmons reaction in one pot, following the addition of an aldehyde, resulted in the production of the 3-alkylidene-1,4-cycloheptadiene derivative. The electrocyclic reaction proceeded in a stereospecific manner, resulting in the stereocontrolled formation of two neighboring stereogenic centers.

Synthesis of Seven-Membered Cross-Conjugated Cyclic Trienes by 8π Electrocyclic Reaction.

A method for the synthesis of 3-methylene-1,4-cycloheptadiene derivatives via an 8π electrocyclization reaction was developed. The triene substrate bearing a phosphate or carbamate group was prepared from γ,δ-unsaturated esters and α,ß-unsaturated aldehydes in four steps. Upon treatment with NaHMDS or KHMDS, the substrate formed a heptatrienyl anion, which underwent electrocyclization and subsequent ß-elimination of the leaving group. The product could be converted into a tropylium salt in two steps.