Synthesis of racemic rosmarinic acid

Racemic rosmarinic acid was prepd. by conversion of 3,4-(OH)(2)C6H2CHO by (i) protection of the OH groups with allyl substituents and reaction with malonic acid to caffeic acid, (ii) parallel condensation with Ac2O, NaOAc and AcNHCH2COOH and subsequent hydrogenation on Pd/C catalyst to racemic 3,4-dihydroxyphenyllactic acid protected then with ally! groups and (iii) coupling of the caffeic and lactic acids in presence of Me2N(CH2)(3)N=C=NEt center dot HCI as coupling agent and finally (iv) catalytic deprotection of OH groups in the presence of Ph3P and Pd(OAc)(2) to the final product. The purity of rosmarinic acid was 96% and its yield 66%.