Synthesis of intermediate (XI): The reaction of 3,5-dimethoxyaniline (I) with ethyl acetoacetate (II) by means of acetic acid in refluxing benzene gives ethyl 3-(3,5-dimethoxyanilino)-2-butenoate (III), which is reduced with NaBH4 in methanol or with H2 over Pt in acetic acid affording ethyl 3-(3,5-dimethoxyanilino)butyrate (IV). The reaction of (IV) with ethyl chloroformate (V) in pyridine yields ethyl 3-(3,5-dimethoxy-N-ethoxycarbonylanilino)butyrate (VI), which is hydrolyzed with diluted NaOH in ethanol giving 3-(3,5-dimethoxy-N-ethoxycarbonylanilino)butyric acid (VII). The cyclization of (VII) with polyphosphoric acid in hot CHCl3 affords 1-ethoxycarbonyl-5,7-dimethoxy-2-methyl-4-oxo-1,2,3,4-tetrahydroquinoline (VIII), which is hydrolyzed with refluxing 48% aqueous HBr to give 5,7-dihydroxy-2-methyl-4-oxo-1,2,3,4-tetrahydroquinoline (XI). The tetrahydroquinolone (XI) can also be obtained by condensation-cyclization of 3,5-dimethoxyaniline (I) with crotonic acid (IX) or its methyl ester (X) by means of acetic acid or pyridine, followed by a treatment with aqueous HBr to hydrolyze the methoxy groups.

The condensation of (XI) with 5-phenyl-2-pentanol (XII) by means of triethylamine in THF yields 5-hydroxy-2-methyl-7-(5-phenyl-2-pentyloxy)-4-oxo-1,2,3,4-tetrahydroquinoline (XIII), which is formylated with ethyl formate by means of NaH affording 1-formyl-5-hydroxy-3-hydroxymethylen-2-methyl-7-(5-phenyl-2-pentyloxy)-4-oxo-1,2,3,4-tetrahydroquinoline (XIV). The reaction of (XIV) with methyl vinyl ketone (XV) by means of triethylamine in methanol yields 1,3-diformyl-5-hydroxy-2-methyl-7-(5-phenyl-2-pentyloxy)-4-oxo-3(3-oxobutyl-1,2,3,4-tetrahydroquinoline (XVI), which by treatment with K2CO3 in ether is converted into 1-formyl-5-hydroxy-2-methyl-7-(5-phenyl-2-pentyloxy)-4-oxo-3(3-oxobutyl-1,2,3,4-tetrahydroquinoline (XVII). The cyclization of (XVII) with KOH in refluxing methanol gives 5,6,6a,7-tetrahydro-1-5-hydroxy-6beta-methyl-3-(5-phenyl-2-pentyloxy)benzo[c]quinoline-9(8H)-one (XVIII), which is treated first with Li in liquid NH3, and then with acetic anhydride to afford 5,6,6a,7,10,10a-hexahydro-1-acetoxy-6beta-methyl-3-(5-phenyl-2-pentyloxy)benzo[c]quinoline-9(8H)-one (XIX). Finally this compound is reduced with NaBH4 in ethanol.

Synthesis of intermediate (XI): The reaction of 3,5-dimethoxyaniline (I) with ethyl acetoacetate (II) by means of acetic acid in refluxing benzene gives ethyl 3-(3,5-dimethoxyanilino)-2-butenoate (III), which is reduced with NaBH4 in methanol or with H2 over Pt in acetic acid affording ethyl 3-(3,5-dimethoxyanilino)butyrate (IV). The reaction of (IV) with ethyl chloroformate (V) in pyridine yields ethyl 3-(3,5-dimethoxy-N-ethoxycarbonylanilino)butyrate (VI), which is hydrolyzed with diluted NaOH in ethanol giving 3-(3,5-dimethoxy-N-ethoxycarbonylanilino)butyric acid (VII). The cyclization of (VII) with polyphosphoric acid in hot CHCl3 affords 1-ethoxycarbonyl-5,7-dimethoxy-2-methyl-4-oxo-1,2,3,4-tetrahydroquinoline (VIII), which is hydrolyzed with refluxing 48% aqueous HBr to give 5,7-dihydroxy-2-methyl-4-oxo-1,2,3,4-tetrahydroquinoline (XI). The tetrahydroquinolone (XI) can also be obtained by condensation-cyclization of 3,5-dimethoxyaniline (I) with crotonic acid (IX) or its methyl ester (X) by means of acetic acid or pyridine, followed by a treatment with aqueous HBr to hydrolyze the methoxy groups.

The condensation of (XI) with 5-phenyl-2-pentanol (XII) by means of triethylamine in THF yields 5-hydroxy-2-methyl-7-(5-phenyl-2-pentyloxy)-4-oxo-1,2,3,4-tetrahydroquinoline (XIII), which is formylated with ethyl formate by means of NaH affording 1-formyl-5-hydroxy-3-hydroxymethylen-2-methyl-7-(5-phenyl-2-pentyloxy)-4-oxo-1,2,3,4-tetrahydroquinoline (XIV). The reaction of (XIV) with methyl vinyl ketone (XV) by means of triethylamine in methanol yields 1,3-diformyl-5-hydroxy-2-methyl-7-(5-phenyl-2-pentyloxy)-4-oxo-3(3-oxobutyl-1,2,3,4-tetrahydroquinoline (XVI), which by treatment with K2CO3 in ether is converted into 1-formyl-5-hydroxy-2-methyl-7-(5-phenyl-2-pentyloxy)-4-oxo-3(3-oxobutyl-1,2,3,4-tetrahydroquinoline (XVII). The cyclization of (XVII) with KOH in refluxing methanol gives 5,6,6a,7-tetrahydro-1-5-hydroxy-6beta-methyl-3-(5-phenyl-2-pentyloxy)benzo[c]quinoline-9(8H)-one (XVIII), which is treated first with Li in liquid NH3, and then with acetic anhydride to afford 5,6,6a,7,10,10a-hexahydro-1-acetoxy-6beta-methyl-3-(5-phenyl-2-pentyloxy)benzo[c]quinoline-9(8H)-one (XIX). Finally this compound is reduced with NaBH4 in ethanol.