A practical, tandem and protecting-group-free synthesis of (+)-rosmarinic acid and its analogues

A short, tandem and protecting-group-free total synthesis of (+)-rosmarinic acid and related ester derivatives from (+)-danshensu (or corresponding aryl lactic acid) and related hydroxybenzaldehydes in 54 %similar to 87 % overall yield is described. The key step is the Meldrum's acid mediate tandem classical Knoevenagel condensation.