1) The reduction of 2-methyl-2-phenylpropionic acid with LiAlH4 in THF gives 2-methyl-2-phenyl-1-propanol (II), which is acetylated with acetic anhydride in pyridine yielding the acetate (III). The Friedel-Crafts condensation of (III) with 4-chlorobutyryl chloride (IV) by means of AlCl3 in dichloromethane affords the butyrophenone (V), which is condensed with alpha,alpha-diphenylipiperidine-4-methanol (VI) by means of KHCO3 and KI in refluxing toluene/water to give the butyrophenone (VII). The deacetylation of (VII) with NaOH in refluxing methanol yields the primary alcohol (VIII), which is oxidized with oxalyl chloride and DMSO in methylene chloride to the corresponding aldehyde (IX). The oxidation of (IX) with KMnO4 in acetone affords the ketoacid (X), which is finally reduced with NaBH4 in water. 2) The acetate (III) can also be obtained by Friedel-Crafts condensation of 2-methyl-2-propenyl acetate (XI) with refluxing benzene (XII) by means of AlCl3. 3) The ketoacid (X) can also be obtained by direct oxidation of the primary alcohol (VIII) with H5IO6 in chloroform/acetonitrile, or K2S2O8 in acetone/acetonitrile, both catalyzed by RuCl3.5H2O.

4) The Friedel-Crafts condensation of cyclopropylcarbonyl chloride (XIII) with 2-methyl-2-phenylpropionic acid ethyl ester (XIV) gives 2-[4-(cyclopropylcarbonyl)phenyl]-2-methylpropionic acid ethyl ester (XV), which by reaction with dry HCl in hot acetonitrile yields the 4-chlorobutyryl derivative (XVI). The condensation of (XVI) with the piperidine (VI) by means of KHCO3 affords the omega-piperidylbutyrophenone (XVII), which is reduced with NaBH4 in methanol to give the dihydroxy ester (XVIII). Finally, this compound is saponified with NaOH in refluxing methanol. 5) The chlorobutyryl derivative (XVI) can also be obtained by direct Friedel-Crafts condensation of propionic ester (XIV) with 4-chlorobutyryl chloride (IV) by means of AlCl3 as before.

The Friedel Craft's condensation of 2-methyl-2-phenylpropionic acid methyl ester (I) with succinic anhydride (II) by means of AlCl3 in CS2 or dichloromethane/nitrobenzene gives 2-[4-(hydroxysuccinyl)phenyl]-2-methylpropionic acid methyl ester (III) (purified through its phenethylamine salt), which is condensed with 4-(1-hydroxy-1,1-diphenylmethyl)piperidine (IV) by means of ethyl chloroformate and TEA in THF or with DCC and p-nitrophenol in ethyl acetate to yield the adduct (V). The reduction of the oxo groups of (V) by means of BH3/Me2S in THF affords the ester precursor (VI), which is finally hydrolyzed with NaOH in refluxing methanol to provide the target compound.

1) The reduction of 2-methyl-2-phenylpropionic acid with LiAlH4 in THF gives 2-methyl-2-phenyl-1-propanol (II), which is acetylated with acetic anhydride in pyridine yielding the acetate (III). The Friedel-Crafts condensation of (III) with 4-chlorobutyryl chloride (IV) by means of AlCl3 in dichloromethane affords the butyrophenone (V), which is condensed with alpha,alpha-diphenylipiperidine-4-methanol (VI) by means of KHCO3 and KI in refluxing toluene/water to give the butyrophenone (VII). The deacetylation of (VII) with NaOH in refluxing methanol yields the primary alcohol (VIII), which is oxidized with oxalyl chloride and DMSO in methylene chloride to the corresponding aldehyde (IX). The oxidation of (IX) with KMnO4 in acetone affords the ketoacid (X), which is finally reduced with NaBH4 in water. 2) The acetate (III) can also be obtained by Friedel-Crafts condensation of 2-methyl-2-propenyl acetate (XI) with refluxing benzene (XII) by means of AlCl3. 3) The ketoacid (X) can also be obtained by direct oxidation of the primary alcohol (VIII) with H5IO6 in chloroform/acetonitrile, or K2S2O8 in acetone/acetonitrile, both catalyzed by RuCl3.5H2O.

4) The Friedel-Crafts condensation of cyclopropylcarbonyl chloride (XIII) with 2-methyl-2-phenylpropionic acid ethyl ester (XIV) gives 2-[4-(cyclopropylcarbonyl)phenyl]-2-methylpropionic acid ethyl ester (XV), which by reaction with dry HCl in hot acetonitrile yields the 4-chlorobutyryl derivative (XVI). The condensation of (XVI) with the piperidine (VI) by means of KHCO3 affords the omega-piperidylbutyrophenone (XVII), which is reduced with NaBH4 in methanol to give the dihydroxy ester (XVIII). Finally, this compound is saponified with NaOH in refluxing methanol. 5) The chlorobutyryl derivative (XVI) can also be obtained by direct Friedel-Crafts condensation of propionic ester (XIV) with 4-chlorobutyryl chloride (IV) by means of AlCl3 as before.

Fexofenadine has been obtained by two new related ways: 1) The Grignard condensation of ethyl 2-(4-formylphenyl)-2-methylpropionate (I) with 2-(1,3-dioxolan-2-yl)ethylmagnesium bromide (II) gives the corresponding carbinol (III), which by a treatment with Amberlyst-15 yields the lactol (IV). The reductocondensation of (IV) with the piperidine derivative (V) by means of NaBH4 in methanol affords the ethyl ester (VI), which is finally hydrolyzed with NaOH. 2) The Grignard condensation of ethyl 2-[4-(chloroformyl)phenyl]-2-methylpropionate (VII) with 2-(1,3-dioxolan-2-yl)ethylmagnesium bromide (II) gives the corresponding ketone (VIII), which is reduced to carbinol (III) in the usual way. 3) The (S)-enantiomer of fexofenadine can be synthesized through the asymmetric reduction of the prochiral ketone (VIII) with chiral catalysts to afford the (S)-enantiomer of carbinol (III).