NATURAL-PRODUCTS SYNTHESIS BY RETRO-DIELS-ALDER REACTION .10. TOTAL SYNTHESIS AND STRUCTURAL REVISION OF CHROMOMORIC ACID C-I AND C-II METHYL-ESTERS

Stereospecific total synthesis of chromomoric acid C-I and C-II methyl esters and delicate elucidation of their structures have been reported. A sterospecific five-step synthesis, starting from enone 5, with one-pot three-component coupling and retro Diels-Alder reaction as the key reactions provided a target molecule which was proved to be chromomoric acid C-I methyl ester (1), but its physical data were identical with that of the natural product originally assigned to be chromomoric acid C-IV methyl ester (4). Structural elucidation with a lanthanide shift reagent showed the original assignment should be revised to 1. Total synthesis and structural confirmation of chromomoric acid C-II methyl ester (2) was thereafter fulfilled.