合成路线1

Intermediate (VII) can be obtained by following two different pathways: 1. Hydrogenation of 4-pyridine acetic acid (IX) over PtO2 in AcOH affords piperidinyl derivative (X), which is then protected with Boc2O and NaOH in THF to yield (XI). Reduction of the CO2H group of (XI) with BH3.THF in THF gives alcohol (XII), which is then subjected to Swern oxidation with oxalyl chloride and DMSO in CH2Cl2, followed by reaction with Wittig reagent (XIII) and N-methyl morpholine (NMM), to provide crotonate (XIV). Hydrogenation of (XIV) over Pd/C in MeOH furnishes methyl butyrate (XV), which is finally hydrolyzed with NaOH in MeOH. 2. Alternatively, intermediate (VII) can be obtained by reaction of diethyl malonate (XVI) with 4-vinylpyridine and NaH in EtOH to afford derivative (XVIII), which is hydrolyzed and decarboxylated with HCl/H2O and then hydrogenated over PtO2 to provide piperidine derivative (XIX). Finally, (XIX) is protected by reaction with Boc2O and NaOH in THF.