SYNTHESIS OF (+ -)-ROSMARINIC ACID METHYLESTER/

Regioselective cleavage of the glycidic ester 3 by BF3/ether to pyruvi c acid ester 4 followed by NaBH4 reduction affords the lactic acid der ivative 5a which in turn can be acylated by caffeoyl chloride 8c to yi eld 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 subsequentl y reacted with the aldehyde 1a. The analogous reaction using the silyl protected educts 7d and 1b failed to give 9d. Finally, 9a is debenzyl ated by BCl3 furnishing the title compound 10a in fair total yield.