Synthetic Studies to exo‐Ring‐Junction based Fused 5/5/n‐Tricyclic Systems: Access to A, B, C‐Ring System of Longeracinphyllin A, Himalenine D, and Daphnipaxiamine A.

We disclose an efficient synthetic sequence to fused tricyclic systems found in various diquinane-based natural products. The fused 5/5/7-tricyclic systems were assembled using ring-rearrangement metathesis as key step. These tricyclic systems are found as a core skeleton in natural products like longeracinphyllins A, himalenine D and daphnipaxianine A, etc.

Abstract

We report a short synthetic approach to various tricyclic systems that are present in several diquinane-based natural products starting with a readily available exo-dicyclopentadiene-1-one. To this end, we have successfully assembled a fused 5/5/7-tricyclic enone via ring-rearrangement metathesis as a key step. The strategy has been further extended to synthesize the 1,3-dihydroxy and then 1-keto-3-hydroxy derivatives by utilizing regio- and stereoselective epoxidation and ring-rearrangement metathesis reactions as key steps. All these target compounds are found to be present in diquinane-based natural products such as longeracinphyllins A, himalenine D and daphnipaxianine A, etc. Moreover, the newly synthesized tricyclic compounds matches the exact ring-junction stereochemistry (5/5-exo) of these natural products. Hence, the synthetic studies disclosed here may be useful in the synthesis of biologically significant natural products and in the drug design. The newly synthesized molecules were characterized by NMR and HRMS data. Some of these structures were confirmed by a single crystal X-ray diffraction studies.

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