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1) The reaction of 4-bromobenzaldehyde (I) with trimethylorthoformate (II) and p-toluenesulfonic acid in methanol gives ketal (III), which is condensed with 2-pyridylmagnesium bromide in THF, yielding 4-(2-pyridyl)benzaldehyde (IV). The reaction of (IV) with tert-butyl carbazate (V) in refluxing ethanol affords hydrazone (VI), which is reduced with H2 over Pd/C in methanol to the hydrazine (VII). The condensation of (VII) with the epoxide (VIII) in hot isopropanol gives the expected addition product (IX), which by treatment with HCl or formic acid results in the fully deprotected intermediate (X). Finally, this compound is condensed with N-(methoxycarbonyl)-L-tert-leucine (XI) by means of O-(2-oxo-1,2-dihydro-1-pyridyl)-N,N,N',N'-tetramethyluronium tetrafluoroborate (TPTU) in dichloromethane or DMF.

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2) Intermediate (IX) can also be obtained as follows: The cyclization of 4-cyanobenzoic acid methyl ester (XII) with acetylene at 15 Atm by means of cobaltocene in toluene at 180 C gives 4-(2-pyridyl)benzoic acid methyl ester (XIII), which is saponified with NaOH in methanol to the corresponding acid (XIV). The activation of (XIV) with isobutyl chloroformate yields the mixed anhydride (XV), which is condensed with N-(tert-butoxycarbonyl)-L-phenylalaninal (XVI) and KCN in dichloromethane, affording (XVII). The reaction of (XVII) with tert-butyl carbazate (V) by means of acetic acid in methanol gives hydrazone (XVIII), which is reduced to hydrazine (XIX) by means of sodium cyanoborohydride in THF. The isomerization of (XIX) by means of 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTDE) in hot diglyme yields hydrazide (XX), which is finally reduced to intermediate (IX) with diisobutylaluminum hydride in dichloromethane/THF.

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The intermediate carbazate (VI) has been obtained as follows. The condensation of phenylboronic acid (I) with 2-bromopyridine (II) by means of Pd(PPh3)4 gives 4-(2-pyridyl)benzaldehyde (III), which is condensed with tert-butyl carbazate (IV) in hot toluene/isopropyl alcohol to yield the benzylidenehydrazone (V). Finally, this compound is reduced with sodium formate over Pd/C in ethanol to afford the target intermediate; the carbazate (VI). The selective monosilylation of the primary OH group of diol (VII) with Tbdms-Cl, TEA and DMAP followed by reaction of the secondary OH group with MsCl gives the protected mesylate (VIII), which is desilylated with NH4F and AcOH yielding the primary alcohol (IX). The epoxidation of (IX) with t-BuOK in isopropyl alcohol affords the chiral epoxide (X), which is condensed with the intermediate carbazate (VI) in refluxing isopropanol to provide the adduct (XI). Elimination of the two Boc protecting groups of (XI) with HCl in hot THF gives the diamino compound (XII), which is finally condensed with two moles of N-(methoxycarbonyl)-L-tert-leucine (XIII) by means of WSC, HOBt and DIEA in dichloromethane to provide the target Atazanavir.