3.4- Diphenyl-2-oxazolidinone

Oxazolidinones have also been used as intermediates in simple transformations utilising their peculiar reactivity. The absolute configuration of WBoc-P-aminoalcohol 213 can be easily inverted via Sn2 cyclisation to oxazolidinone 214 <00TL10071>. Treatment with Olah s reagent (HF-Pyridine) of 4-alkyl-5,5-diphenyl-oxazolidinones 216 afforded the corresponding a-(fluorodiphenylmethyl)alkylamines 217 <00TA2033>. 

This imide system can also be used for the asymmetric synthesis of optically pure a,a-disubstituted amino aldehydes, which can be used in many synthetic applications.31 These optically active a-amino aldehydes were originally obtained from naturally occurring amino acids, which limited their availability. Thus, Wenglowsky and Hegedus32 reported a more practical route to a-amino aldehydes via an oxazolidinone method. As shown in Scheme 2 20, chiral diphenyl oxazolidinone 26 is first converted to allylic oxazolidinone 27 subsequent ozonolysis and imine formation lead to compound 28, which is ready for the a-alkylation using the oxazolidinone method. The results are shown in Table 2-6. 

The diphenyl oxazolidinone, 15, in combination with Lewis acids provides a general solution for diastereoselective reactions. Sibi has prepared the diphenyl-oxazolidinone in three steps from the methyl ester of serine (the hydrochloride) as shown in Scheme 1 [23, 24]. The overall yield for the sequence is 60%, and both enantiomers are available from commercially available starting materials. The oxazolidinone itself is now commercially available. 

Annual Volume 71 contains 30 checked and edited experimental procedures that illustrate important new synthetic methods or describe the preparation of particularly useful chemicals. This compilation begins with procedures exemplifying three important methods for preparing enantiomerically pure substances by asymmetric catalysis. The preparation of (R)-(-)-METHYL 3-HYDROXYBUTANOATE details the convenient preparation of a BINAP-ruthenium catalyst that is broadly useful for the asymmetric reduction of p-ketoesters. Catalysis of the carbonyl ene reaction by a chiral Lewis acid, in this case a binapthol-derived titanium catalyst, is illustrated in the preparation of METHYL (2R)-2-HYDROXY-4-PHENYL-4-PENTENOATE. The enantiomerically pure diamines, (1 R,2R)-(+)- AND (1S,2S)-(-)-1,2-DIPHENYL-1,2-ETHYLENEDIAMINE, are useful for a variety of asymmetric transformations hydrogenations, Michael additions, osmylations, epoxidations, allylations, aldol condensations and Diels-Alder reactions. Promotion of the Diels-Alder reaction with a diaminoalane derived from the (S,S)-diamine is demonstrated in the synthesis of (1S,endo)-3-(BICYCLO[2.2.1]HEPT-5-EN-2-YLCARBONYL)-2-OXAZOLIDINONE. 

B. (4R,5S)-3-(1-Methoxyethyl)-4,5-diphenyl-2-oxazolidinone. A 2-L, threenecked, round-bottomed flask equipped with a magnetic stirrer, thermometer, and a reflux condenser is charged with (4R,5S)-4,5-diphenyl-2-oxazolidinone (20.0 g, 84 mmol), ( )-10-camphorsulfonic acid (9.7 g, 42 mmol) (Note 7), and acetaldehyde dimethyl acetal (700 mL) (Note 8). The mixture is heated at gentle reflux in an oil bath (bath temperature 80°C) for 5 hr (Note 9). The mixture is allowed to cool to ambient temperature, then concentrated under reduced pressure on a rotary evaporator (Note 10). Ethyl acetate (100 mL) is added to the residue, and the ethyl acetate solution is transferred to a beaker. The solution is neutralized with saturated sodium bicarbonate solution (100 mL) (Note 11), and transferred into a separatory funnel. The two layers are separated, and the lower aqueous layer is extracted with ethyl acetate (100 mL). 

Hegedus and co-workers8 reported the synthesis of (4S,5R)-4,5-diphenyl-3-vinyl-2-oxazolidinone (the enantiomer of the compound prepared here) via the chromium carbene complex in a fair yield. This is an interesting method, but the procedure is complicated (e.g., low temperature, argon atomsphere) and the chromium waste must be disposed of in an appropriate way. On the other hand, this procedure, consisting of transacetalization9 and pyrolysis,10 is simple and safe. Optically active 3-vinyl-2-oxazolidinone is also used for the synthesis of (1 R,2S)-2-fluorocyclopropylamine11a b that is the key intermediate for novel antibacterial quinolonecarboxylic acids. 

S,5R)-4,5-Diphenyl-3-vinyl-2-oxazolidinone 2-Oxazolidinone, 3-ethenyl-4,5-diphenyl-, (4S-cis)- (12) (128947-27-3)... 

The organic layers are combined, washed with brine, dried over anhydrous sodium sulfate, filtered, then concentrated under reduced pressure on a rotary evaporator. The residue is stirred with 2-propanol-hexane (1 1,60 mL) for several minutes. The solid product is collected by filtration. The filtrate is concentrated on a rotary evaporator, and the residue is again stirred with 2-propanol-hexane (1 1, 5 mL). The precipitate is collected by filtration. The two lots of the products are dried in a desiccator over phosphorus pentoxide (P2O5) under reduced pressure for 12 hr. (4R,5S)-3-(Methoxyethyl)-4,5-diphenyl-2-oxazolidinone (22.2 g, 89.3%) (Note 12) is obtained as a diastereomeric mixture. In some runs, small amounts of impurities remained after trituration. These impurities can be carried through the next step without a problem although final yields will be reduced. 

C. (4R,5S)-4,5-Diphenyl-3-vinyl-2-oxazolidinone. A 500-mL filter flask is charged with (4R,5S)-3-(1-methoxyethyl)-4,5-diphenyl-2-oxazolidinone (8.9 g, 30 mmol) and solid ammonium chloride, NH4CI (0.32 g, 6.0 mmol). The flask is stoppered and heated behind a blast shield in a sand bath to 150°C - 170°C under reduced pressure via a water aspirator (ca. 11 mm) for 3 hr. The crude material is dissolved in CH2CI2 and run through silica gel with CH2CI2 (40 g of SiC>2, 250 mL of CH2CI2) to afford the product as a white solid (6.68 g, 84.2%) (Note 13). (A second treatment with silica is sometimes required to give completely clean product.)... 

Optically active 2-oxazolidinones and 2-thiazolidinones are versatile compounds as chiral auxiliaries. 5a b (4R,5S)-4,5-Diphenyl-2-oxazolidinone has been used for the synthesis of optically active amines6 because of its high stereoselectivity and easy deprotection by hydrogenolysis after the reaction. Compared with several preparations73-0 of (4R,5S)-4,5-diphenyl-2-oxazolidinone reported so far, this method,... 

If the two described aminoteUurinylation procedures are performed at a higher temperature, tellurium-free products are obtained in high yields 2-oxazolidinones and 2-oxa-zolines, respectively. Diphenyl ditelluride is formed as by-product. These heterocycles constitute an important class of compounds with wide applications. 

A. (4R,5S)-4,5-Diphenyl-2-oxazolidinone. A 1-L, three-necked, round-bottomed flask equipped with a magnetic stirrer, thermometer, reflux condenser, and a dropping funnel is charged with (1S,2R)-(+)-2-amino-1,2-diphenylethanol (20.0 g, 94 mmol) (Note 1) and dichloromethane, CH2CI2, (140 mL), and cooled in an ice-water bath. After addition of triethylamine (28.4 mL, 204 mmol), a solution of triphosgene [bis... 

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