EXPERIMENTS DIRECTED TOWARD TOTAL SYNTHESIS OF TERPENES .13. CONSTRUCTION OF LACTONE RING OF ROSENONOLACTONE

The use of the lead tetraacetate-iodine transannular oxidation has been explored as a method forthe construction of the lactone bridge of rosenonolactone (2). Attempts were made to isomerize the 9β→12 lactone 20, formed on oxidation of the 9β alcohol 16, to the requisite 4bβ→12 lactone 6 under acid conditions with no success. The 9β→12 ether 18, also available from the same precursor on oxidation with lead tetraacetate alone, could only be cleaved so as to generate the chlorodiacetate 27. Oxidation of the 12-hydroxyacetate 30, obtained in 20% yield by an alternate synthetic scheme from the aromatic enone 33, with lead tetraacetate iodine established the desired oxygen bridge in 28% yield. The acetoxylactone 6 could then be obtained in 50% yield by further chromic acid oxidation of the ether. © 1969, American Chemical Society. All rights reserved.