Synthesis and Structure Revision of Dichrocephones†A and B.

Herein, we report the first enantioselective synthesis of dichrocephones A and B, which are cytotoxic triquinane sesquiterpenes with a dense array of stereogenic centers within a strained polycyclic environment. Key features include the application of a catalytic asymmetric Wittig reaction, followed by stereoselective functionalization of the propellane core into a pentacyclic intermediate. Double reductive ring cleavage yielded the proposed structure of dichrocephone A. Mismatched spectroscopic data for our synthetic material compared to the natural isolate led us to revise the previously proposed configuration based on biosynthetic considerations and NMR calculations. Implementation of these findings culminated in the synthesis of dichrocephones A and B.