合成路线1

The intermediate aldehyde (XXV) has been prepared by two related procedures. Benzylic bromination of o-tolylacetic acid (XIV) employing NBS and AIBN leads to bromo acid (XV), which is further converted into the tert-butyl ester (XVI) upon treatment with isobutylene and sulfuric acid. Bromide group displacement in (XVI) with NaN3 in hot DMF affords azide (XVII). This is then reduced by catalytic hydrogenation to the corresponding primary amine, which can be isolated as the more stable oxalate salt (XVIII). After protection of amine (XVIII) as the N-Boc derivative (XIX), selective reduction of the ester function employing LiAlH4 in cold Et2O gives rise to alcohol (XX). Further bromination of alcohol (XX) to produce (XXI) is accomplished by treatment with CBr4 and PPh3. Bromide (XXI) is condensed with 3-amino-1-propanol (XXII) yielding amino alcohol (XXIII), which is subsequently protected as the di-Boc derivative (XXIV). Swern oxidation of alcohol (XXIV) generates the required aldehyde intermediate (XXV).