A general approach to cyathin diterpenes.: Total synthesis of allocyathin B3

[GRAPHICS] The synthesis of allocyathin B-3 from an advanced intermediate possessing the ring system and relative stereochemistry but tacking the isopropyl and hydroxymethyl groups is reported. The isopropyl group was introduced by radical cyclization of a methyl propargyl acetal of an or-bromo ketone, and the hydroxymethyl group was generated by Pd-catalyzed carbonylation of a vinyl triflate. The route provides functionalized intermediates that could allow access to more complex members of the cyathin family of diterpenes.