Dibenzoyl-D-tartaric acid

S-Isomer was prepared the next way. To a solution of 160 parts of dibenzoyl d-tartaric acid in 1600 parts of anhydrous ethanol were added for 15 minutes 80 parts of dl-l-(3-trifluoromethylphenyl)-2-ethylaminopropane. After 15 additional minutes, 90.5 parts of crystalline solid were isolated. When this product was recrystallized from 1300 parts of anhydrous ethanol, there was obtained 70 parts of dibenzoyl d-tartarate acid salt of L-l-(3-trifluoromethylphenyl)-2-ethylaminopropane. This salt was treated with 500 parts of 4 N NaOH. The mixture was extracted with 2x200-part portions of diethyl ether and the ether extract was re-extracted with 100 parts of 4 N hydrodiboric acid. After treatment with 120 parts of 4 N NaOH, the free amine amounting to 25 parts distills at 105°-107°C (17.5 mm.). [a]D25 - 9.6° (c=8% in ethanol). 

Optically active cathinone has been obtained through the optical resolution of racemic norephedrine using 0,C>-dibenzoyl-D-tartaric acid (26). Each enantiomer was formylated (9) and oxidized with chromium trioxide in pyridine, and the product (13) was then deformylated by heating with 20% hydrochloric acid at 40 C (Scheme 2). Estimation of the optical purity by formation of a urea (14) with (—)-l-phenylethyl isocyanate and HPLC scrutiny, showed an optical purity exceeding 98% for each enantiomer. Cathinone as the free base racemizes and dimerizes readily in hydroxylic media, and similar behavior, at a somewhat reduced rate, is also observed for solutions of the oxalate salt sometimes used for isolation purposes. Cathinone base is fairly stable in dilute solution in nonhydroxy lie, nonpolar media. It readily decomposes during drying of the leaf, hence the desire to use fresh material for hedonistic purposes 14,27). 

Scheme 51. Synthesis of [2.2]PHANEPHOS a) 1. 4.2 equiv. BuLi 2. 2.3 equiv. MgBr2Et20 3. Ph2P(0)Cl b) 1. Dibenzoyl-d-tartaric acid 2. NaOH 3. HSiCl3 [102]...

J. Org. Chem., 62, 5452. [(Rp)-PHANEPHOS used in this procedure is actually the diphosphine derivative of dibromo-Pc after resolution of the diphosphine oxide with dibenzoyl-D-tartaric acid]. 

The enantioselective synthesis of MK-4305 93 was achieved with the help of classic resolution by using a chiral dibenzoyl-D-tartaric acid (DBT) for resolving the racemic amine intermediate 96. By tedious optimization of the resolution protocol changing the solvent and antisolvent systems, excellent enantioselectivity could be achieved by using 1.85 equivalents of the chiral DBT and a mixture of tetrahydrofuran and dichloromethane as the solvent system. 

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