合成路线1

2) The condensation of 4-fluorophenol (I) with ethyl (S)-lactate (II) by means of diethyl azodicarboxylate and triphenylphosphine in THF gives ethyl 2(R)-(4-fluorophenoxy)propionate (III), which is reduced with LiAlH4 in THF yielding 2(R)-(4-fluorophenoxy)propanol (IV). The reaction of (IV) with Br2 and triphenylphosphine in DMF affords 1-bromo-2(R)-(4-fluorophenoxy)propane (V), which is condensed with N-benzoyl-2-hydroxyglycine (VI) by means of methanesulfonic acid to give (RS)-N-benzoyl-2-[2-(1-bromo-2(R)propoxy)-5-fluorophenyl]glycine (VII). The cyclization of (VII) by means of acetic anhydride and K2CO3 in acetone yields 6-fluoro-2(R)-methyl-2'-phenylspiro[2,3-dihydro-4H-1-benzopyran-4(RS),4'-oxazolidin]-5'-one (VIII), which is hydrolyzed with refluxing formic acid-HCl affording 4(RS)-amino-6-fluoro-2(R)-methyl-2,3-dihydro-4H-1-benzopyran-4-carboxylic acid (IX). The esterification of (IX) with Cl2SO and methanol gives the corresponding methyl ester (X), which is submitted to optical resolution with alpha-chymotrypsine to yield methyl 4(S)-amino-6-fluoro-2(R)-methyl-2,3-dihydro-4H-1-benzopyran-4-carboxylate (XI). Finally, this compound is cyclized with sodium cyanate in acetic acid.