Synthesis of (S)-ktedonoketone

Total Synthesis of the Diterpenes (+)-Randainin D and (+)-Barekoxide via Photoredox-Catalyzed Deoxygenative Allylation

We report the first enantioselective total synthesis of diterpenoid randainin D, which possesses a hydroazulenone core with a β-substituted butenolide moiety on the cycloheptane ring. The trans-5/7 ring system was formed via a highly challenging ring-closing metathesis delivering the tetrasubstituted cycloheptenone. The butenolide moiety was installed via a novel deoxygenative allylation under Ir-photoredox catalysis, employing methyl oxalate as a red/ox tag. Moreover, the developed allylation was successfully utilized in the 7-step total synthesis of (+)-barekoxide. This study suggests that this deoxygenative allylation method is a promising strategy for the formation of Cq-C(sp3) bonds (Cq = quaternary center) in the context of natural product synthesis.

Unexpected reversal of stereochemistry observed in the addition of methallyltrimethylsilane to a chiral α-keto imide

A Lewis acid-promoted nucleophilic addition of methallyltrimethylsilane to a chiral α-keto imide proceeded with stereoselectivity opposite to that predicted from Soai's report. The difference in the structure of α-keto imides between Soai's and our cases might have affected the diastereofacial selectivity.