BUTENOLIDE ANNELATIONS USING A MANGANESE(III) OXIDATION - A SYNTHESISOF JOLKINOLIDE-E

A general procedure was developed for the annelation of a butenolide t o an enone that highlighted a manganese(III) oxidation of an enone. Th e merit of this procedure was illustrated in a synthesis of (-)-jolkin olide E, ent-1, from (+)-manool 11. A potassium permanganate-mediated degradation of 11 and dehydration of an intermediate beta-hydroxyketon e 12 according to a literature procedure afforded a tricyclic enone 13 . Oxidation of 13 with manganese(III) acetate and chloropropionic acid regio- and stereoselectively furnished a C-12 alpha chloropropionyl e ster 14. An Arbuzov reaction of 14 with triethylphosphite and an intra molecular Horner-Emmons cyclization of the resulting phosphonate 15 ga ve (-)-jolkinolide E, the structure of which was investigated in detai l by NMR. This methodology was also applied to 4,4-dimethylcyclohex-2- en-1-one. This overall approach offers a general solution to the probl em of butenolide annelation to enones.