Synthesis of (±)-Rosmarinic Acid Methylester

Article abstract of DOI:10.1007/BF00806966

Regioselective cleavage of the glycidic ester 3 by BF₃/ether to pyruvic acid ester 4 followed by NaBH₄ reduction affords the lactic acid derivative 5a which in turn can be acylated by caffeoyl chloride 8c to yield the O-protected rosmarinic acid ester 9a. Alternatively, 9a can be prepared by acylation of 5a with diethylphosphono acetyl chloride (6c) thus generating the Wadsworth-Emmons reagent 7a which is subsequently reacted with the aldehyde 1a. The analogous reaction using the silyl protected educts 7d and 1b failed to give 9d. Finally, 9a is debenzylated by BCl₃ furnishing the title compound 10a in fair total yield.