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The Example of preparing (R)-succinic acid(cas:110-15-6) derivatives
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Release time：2016/8/9 17:30:50
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The optical purity of 2(R)-benzylsuccinic acid derivatives was determined by conversion to 2(R)-benzylsuccinic acid by hydrolysis with aqueous lithium hydroxide in methanol. After isolation of the acid, the optical rotation was obtained and compared to the value of optically pure 2(R)-benzylsuccinic acid, [alpha]25 D=+27° (c=2.0, ethyl acetate). See Cohen, S. G.; Milovanovic, A. J. Am. Chem. Soc. 1968, 90, 3495.
Optical purity can also be determined by the addition of the chiral NMR shift reagent tris[3-(heptafluorobutyryl)d-camphorato]europium III to a solution of the succinic acid methyl ester in deuteriochloroform and then integration of the methyl ester resonance, or by HPLC analysis on a Chiracel OC column eluting with hexane:isopropyl alcohol solvent (98:2 volume to volume ratio) at 1 mL/minute monitoring at 210 nm.
EXAMPLE I
Preparation of 2(E)-Isobutylidene Mono-Methyl Succinate by Stobbe Condensation
A 1000 mL round-bottomed flask equipped with a reflux condenser, nitrogen inlet, constant pressure addition funnel and mechanical stirrer was charged with tert-butyl alcohol (300 mL) and then potassium tert-butoxide (Aldrich) (49.4 g, 0.44 mol) was added portion wise over ca. 0.5 hour (this prevents clumping of the tert-butoxide). To this stirring solution was added dropwise over ca. 45 minutes a solution of isobutyraldehyde (28.1 g, 0.4 mol) and dimethyl succinate (73.1 g, 0.5 mol) in 50 mL of tert-butyl alcohol. The solution was then warmed to 50° C. for a period of 2 h and then concentrated on a rotary evaporator. The thick oil was diluted with 3N HCl, then extracted with ether (3×100 mL), and the combined ethereal layer was then extracted with saturated aqueous sodium bicarbonate (3×100 mL). The combined aqueous extract was then acidified to pH=1 with HCl and re-extracted with ether (3×100 mL). The combined ethereal phase was washed with brine and dried over anhydrous magnesium sulfate, filtered, and stripped on a rotary evaporator. The last traces of ether were removed on a vacuum pump overnight. In the morning the crude product had solidified into a white mass, 66.2 g 89% yield. The nmr of this material showed that some of the undesired (Z)-isomer was present, ca. 15% The crude solid was crushed and then washed with n-hexane. This removed the oily substance that was trapped on the solid, providing a nice free flowing powder. The solid was taken up in 290 mL of boiling hexane and allowed to stand. The product initially oiled out but with some swirling and scratching crystallized. The material was then isolated by filtration on a Buchner funnel, was washed with some cold hexane, and then dried in a vacuum drying oven for a couple of hours. The material thus obtained was a very nice free flowing powder that gave a nmr consistent with the desired product, mp 72°-74° C., total yield 46 g, 62%.
Asymmetric Reduction of 2(E)-Isobutylidene mono-Methyl Succinate,
Preparation of 2(R)-Isobutyl Mono-Methyl Succinate
A Fisher-Porter bottle was charged with the above mono-methyl ester (10.00 g, 0.0538 mol), 50 mL of degassed methanol, and 300 mg of rhodium (R,R)DiPAMP (R,R)-(1,2-ethanediyl bis[(O-methoxyphenyl)phenylphosphine]) catalyst. After 5 nitrogen purges (40 psig) the solution was purged 5× with hydrogen (40 psig) and then allowed to hydrogenate at room temperature for 24 h. The hydrogen was displaced with nitrogen and the bottle opened and the methanol removed on a rotary evaporator. The catalyst was removed by passing through a silica gel column eluting with hexane/ethyl acetate 1:1. Removal of the solvent gave the crude product as an oil. The oil was pumped on a vacuum pump for ca. 1 h and nmr was obtained that looked perfect for the reduced compound. A sample dissolved in ethyl acetate had a specific rotation [α]D20 =+14.9°, 9.60 g, 95%.
EXAMPLE 2
Preparation of 2(E)-Benzylidene Dimethyl Succinate by Heck Reaction,
Palladium Catalyzed Coupling of Dimethyl Itaconate with Iodobenzene
A 250 mL 3-necked round-bottomed flask equipped with reflux condenser, N2 inlet and mechanical stirrer was charged with iodobenzene (40.8 g, 0.2 mol), dimethyl itaconate (31.6 g, 0.2 mol), triethylamine (25.2 g, 0.25 mol) palladium (II) acetate (0.448 g, 2.0 mmol), and triphenylphosphine(1.04 g, 4.0 mmol). The mixture was heated to 100° C. for 6 h whereupon the reaction mixture formed a dark paste. The mixture was cooled to ambient temperature, diluted with ethyl acetate and then poured into a separatory funnel. The solution was washed with 3N HCl, water, saturated aqueous NaHCO3, brine and dried over anhydrous M9 SO4. The solution was filtered, concentrated on a rotary evaporator and the residue vacuum distilled through a 12" Vigeraux column; recovered 6.34 g of dimethyl itaconate, bp 55°-70° D., 0.1 mm and then the desired product boiled at 138° C. 0.1 mm to give 34.25 g, 84% based on recovered dimethyl itaconate.
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