A general approach to cyathin diterpenes. Total synthesis of allocyathin B-3

[GRAPHICS] The synthesis of allocyathin B-3 from an advanced intermediate possessing t he ring system and relative stereochemistry but tacking the isopropyl and h ydroxymethyl groups is reported. The isopropyl group was introduced by radi cal 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.