合成路线1

Synthesis of intermediate (I):
N-Protection of 2-piperidone (VIII) with PMB-Cl using KOH and TBAB in toluene gives N-PMB-2-piperidone (IX), which is then hydrolyzed with NaOH to afford 5-(4-methoxybenzylamino)pentanoic acid (X). Condensation of amine (X) with 5-bromo-2-fluorobenzaldehyde (XI) by means of Na2CO3 in DMSO/H2O then provides the tertiary amine (XII). Methylation of carboxylic acid (XII) with MeI in the presence of K2CO3 leads to the corresponding methyl ester (XIII), which then undergoes intramolecular cyclization by means of NaOMe and CO(OMe)2 to yield the N-PMB-1-benzazocine derivative (XIV). Debenzylation of compound (XIV) by means of TFA in toluene affords N-unsubstituted benzazocine (XV), which is then reductocondensed with isobutyraldehyde (XVI) by means of NaBH(OAc)3 in CH2Cl2, affording the 1-isobutyl derivative (XVII). Suzuki coupling of the 8-bromo-1-benzazocine derivative (XVII) with 4-(2-butoxyethoxy)phenylboronic acid (XVIII) by means of Pd(PPh3)4 provides adduct (XIX). Finally, hydrolysis of methyl ester (XIX) with NaOH in THF/MeOH gives the target carboxylic acid (I) (3). Scheme 2.