Synthesis of key intermediates for a concise and convergent approach to the marine natural product eleutherobin

Synthesis of 1,6-syn-5,6-anti-2-methyl-5-isopropyl-bicyclo[4.3.0]-non-2-en-8-one in three steps from (rac)-phellandrene; and 1,6-syn-1-methyl-6-methoxy-3-aza-9-oxabicyclo[4.2.1]-non-7-en-4-one in five steps from 2-methoxy-5-methylfuran and tetrabromoacetone, provided these key intermediates for the construction of the skeleton of eleutherobin.