合成路线1

The cyclization of (S)-glutamic acid (I) by means of H2SO4 and NaNO2 gives the gamma lactone (II), which is treated with hot SOCl2 to yield the corresponding acyl chloride (III). The reaction of (III) with 4-methoxybenzylamine (IV) affords the expected amide (V), which is submitted to rearrangement in the presence of t-BuOK in THF to provide piperidinedione (VI). The reaction of (VI) with Tbdps-Cl and imidazole gives the silyl ether (VII), which is reduced with NaBH4 in methanol to yield a mixture of regioisomers (VIII). The phenyl migration in (VIII) was easily promoted by reaction with BF3/Et2O through the nonisolated intermediate cis-(IX) to yield (X). The reduction of (X) by means of LiAlH4 in THF affords the N-protected hydroxypiperidine (XI), which is deprotected by hydrogenation with H2 over Pd/C in ethanol to provide the free hydroxypiperidine (XII). The reprotection of (XII) with Boc2O gives the carbamate-protected piperidine (XIII), which is oxidized by means of DMSO, (COCl)2 and DIEA in dichloromethane to yield piperidone (XIV). The reaction of (XIV) with NH2OH and K2CO3 affords the corresponding oxime (XV), which is treated with Ac2O in THF to provide the O-acetyloxime (XVI). The reduction of (XVI) with BH3/Me2S in hot THF gives the expected amine (XVII), which is condensed with 2-methoxybenzaldehyde (XVIII) in THF to yield the imine (XIX). The reduction of (XIX) with NaBH4 in methanol affords the protected benzylamine (XX), which is finally deprotected by means of HCl in methanol to provide CP-99,994.