The condensation of trifluoroacetoacetic acid ethyl ester (I) with cyclohexane-1,3-dione (II) and 3-cyanobenzaldehyde (III) by means of ammonium acetate in refluxing ethanol gives the octahydroquinolone (IV), which is hydrolyzed at its ester group by means of LiOH in hot ethanol/water to yield the corresponding carboxylic acid (V). Finally, this compound is dehydrated by means of TsOH in refluxing toluene to afford the target intermediate (rac)-4-(3-cyanophenyl)-5-oxo-2-(trifluoromethyl)-1,4,5,6,7,8-hexahydroquinoline-3-carboxylic acid (VI).
The reaction of trifluoroacetoacetic acid ethyl ester (I) with (?)-isoborneol (II) at 130 C gives the corresponding isobornyl ester (III), which is condensed with cyclohexane-1,3-dione (IV) and 3-cyanobenzaldehyde (V) by means of ammonium acetate in refluxing ethanol to yield the octahydroquinolone (VI). The hydrolysis of the ester group of (VI), with simultaneous dehydration by means of TsOH in refluxing toluene affords 4-(3-cyanophenyl)-5-oxo-2-(trifluoromethyl)-1,4,5,6,7,8-hexahydroquinoline-3-carboxylic acid (VII) as a racemic mixture. Optical resolution of (VII) through the diastereomeric salt with 1(S)-phenylethylamine (VIII) in toluene/butanol provides the desired isomer (IX), which is finally decarboxylated in N-methyl-2-pyrrolidone at 210 C to furnish the target hexahydroquinolone.
The condensation of 3-cyanobenzaldehyde (I) with trifluoroacetone (II) in piperidine gives 3-(4,4,4-trifluoro-3-oxo-2-butenyl)benzonitrile (III). The condensation of cyclohexane-1,3-dione (IV) with 1(R)-phenylethylamine (V) in refluxing toluene or THF yields the secondary enamine (VI), which is condensed with benzonitrile (III) by means of Tms-Cl in hot acetonitrile to afford the chiral adduct (VII). The cyclization of (VII) by means of NH3 in hot acetonitrile provides the chiral octahydroquinolone (VIII), which is finally dehydrated by means of TFA, MsOH, TsOH or HCl in refluxing acetonitrile to give the target hexahydroquinolone.