合成路线1

The condensation of 4-(benzyloxy)benzaldehyde (XII) with phosphonium salt (V) by means of TMG as before gives the acrylic ester (XIII), which is hydrogenated with H2 over Rh/C in methanol to yield the propionic ester (XIV). The hydrolysis of (XIV) with LiOH in dioxane/water affords the corresponding acid (XV) as a racemic mixture, which is condensed with (R)-phenylglycinol (IX) by means of EDC, HOBt and DIEA in dichloromethane to provide the amide (XVI) as a diastereomeric mixture that is separated by crystallization and chromatography. The desired (S)-isomer (XVII) is treated with H2SO4 in hot dioxane/water to furnish the chiral propionic acid (XVIII), which is esterified with EtOH and HCl to give the ethyl propionate (XIX). The hydrogenolysis of the benzyl ether group of (XIX) with H2 over Pd/C in ethyl acetate yields the phenolic derivative (XX), which is condensed with the bis-methanesulfonate by means of K2CO3 in acetonitrile to afford the adduct (XXI). Finally, the ester group of (XXI) is hydrolyzed with LiOH in THF/water to provide the target propionic acid.