New preparation method of (2E)-2-cyano-3-(3,4-dihydroxy-5-nitrobenzene)-N,N-diethyl-2-acrylamide

The invention discloses a new method for preparing (2E)-2-cyano-3-(3, 4-dihydroxy-5-nitrobenzene)-N, N-diethyl-2-acrylamide (I) of which purity is more than 99.9% and Z-isomer content is 0.01%. The method comprises the steps of: condensing 3, 4-dihydroxy-5-nitrobenzaldehyde (II) with N, N-diethylcyanoacetamide (III) in the presence of mixed solvent and alkali (B) to obtain entacapone salt (IV), and dissolving the obtained compound (IV) through acid in proper solvent to obtain entacapone (I) with pure enantiomers. The method disclosed by the invention has high yield, environmental friend and mild reaction conditions and is suitable for large-scale industrial production.