合成路线1

Intermediates (II) and (IV) are prepared as follows. Alkylation of the sodium enolate of methyl 3-bromophenylacetate (VII) with 4-chlorobenzyl bromide (VIII) in cold THF followed by methyl ester hydrolysis with LiOH in aqueous acetonitrile affords 2-(m-bromophenyl)-3-(p-chlorophenyl)propionic acid (IX), which is converted to the corresponding Weinreb amide (X) by chlorination with oxalyl chloride and subsequent treatment with N,O-dimethylhydroxylamine. Addition of methylmagnesium bromide to the methoxyamide (X) gives the 3,4-diaryl-2-butanone (XI), which is then reduced using NaBH4 or LiBH(s-Bu)3 (L-selectride) to provide alcohol (XIIa) as the major diastereoisomer. After conversion of alcohol (XIIa) to the corresponding mesylate, displacement with NaN3 in hot DMF leads to azide (XIII), which is reduced by catalytic hydrogenation in the presence of PtO2 and Boc2O to afford the Boc-protected amine (XIV). Then, palladium-catalyzed substitution of the aryl bromide (XIV) with zinc cyanide yields the nitrile (XV), which is deprotected to (IIa) using HCl in EtOAc (2, 3). Similarly, coupling between 3-bromobenzonitrile (XVI) and isopropenyl acetate (XVII) in the presence of Pd2(dba)3 and 2-(dicyclohexylphosphino)-2’-(dimethylamino)biphenyl (DCPDMAB) gives 1-(m-cyanophenyl)acetone (XVIII), which is alkylated with 3-chlorobenzyl chloride (XIX) in the presence of cesium hydroxide and tetrabutylammonium iodide to yield the diarylbutanone (XX). Reduction of ketone (XX) with lithium tri(sec-butyl)borohydride produces alcohol (XXI), which is converted to the Boc-protected amine (XV) by mesylation followed by displacement with NaN3, and then reduction of the resulting azide (XXII) by catalytic hydrogenation in the presence of PtO2 and Boc2O (1). The ketonitrile (XX) is alternatively produced by palladium-catalyzed cyanuration of aryl bromide (XI) with either zinc cyanide or potassium ferrocyanide. The intermediate enol tosylate (IV) can be obtained by treatment of (XX) with sodium tert-butoxide and p-toluenesulfonic anhydride (5, 6). Preparation of the enantiomerically pure amine (IIb) can be accomplished by resolution at the stage of the diarylpropionic acid (IX) or, in a more efficient method, by dynamic kinetic resolution of (XI) via stereoselective hydrogenation to (XIIb) in the presence of the chiral Ru catalyst [(S)-xyl-BINAP]-[(S)-DAIPEN]RuCl2 and excess potassium tert-butoxide (4). Scheme 2.