Oxazolidinones catalysis

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. 

Novel aldol-type reactions under Cinchona-deriwed chiral thiourea catalysis was reported by Wang et al. [78]. In their report, a novel cascade Michael-aldol reaction was presented. The reaction involves a tandem reaction catalyzed via hydrogen-bonding with as little as 1 mol% catalyst loading to generate a product with three stereogenic centers (Scheme 28). hi the reaction of 2-mercaptobenzaldehyde 128 and a,P-unsatnrated oxazolidinone 129, the desired benzothiopyran 130 was formed smoothly in high yield and excellent stereoselectivity. 

The initial work on the asymmetric [4-1-2] cycloaddition reactions of A -sulfinyl compounds and dienes was performed with chiral titanium catalysts, but low ee s were observed <2002TA2407, 2001TA2937, 2000TL3743>. A great improvement in the enantioselectivity for the reaction of AT-sulfinyl dienophiles 249 or 250 and acyclic diene 251 or 1,3-cyclohexadiene 252 was observed in the processes involving catalysis with Cu(ll) and Zn(ii) complexes of Evans bis(oxazolidinone) (BOX) ligands 253 and 254 <2004JOC7198> (Scheme 34). While the preparation of enantio-merically enriched hetero-Diels-Alder adduct 255 requires a stoichometric amount of chiral Lewis acid complex, a catalytic asymmetric synthesis of 44 is achieved upon the addition of TMSOTf. 

Yamamoto and co-workers (135,135-137) recently reported a new method for stereocontrol in nitrile oxide cycloadditions. Metal ion-catalyzed diastereoselective asymmetric reactions using chiral electron-deficient dipolarophiles have remained unreported except for reactions using a-methylene-p-hydroxy esters, which were described in Section 11.2.2.6. Although synthetically very useful and, hence, attractive as an entry to the asymmetric synthesis of 2-isoxazohnes, the application of Lewis acid catalysis to nitrile oxide cycloadditions with 4-chiral 3-(2-aIkenoyl)-2-oxazolidinones has been unsuccessful, even when > 1 equiv of Lewis acids are employed. However, as shown in the Scheme 11.37, diastereoselectivities in favor of the ffc-cycloadducts are improved (diastereomer ratio = 96 4) when the reactions are performed in dichloromethane in the presence of 1 equiv of MgBr2 at higher than normal concentrations (0.25 vs 0.083 M) (140). The Lewis acid... 

The first effective enantioselective 1,3-dipolar cycloaddition of diazoalkanes catalyzed by chiral Lewis acids was reported in the year 2000 (139). Under catalysis using zinc or magnesium complexes and the chiral ligand (/ ,/ )-DBFOX/Ph, the reaction of diazo(trimethylsilyl)methane with 3-alkenoyl-2-oxazolidin-2-one 75 (R2 = H) gave the desilylated A2-pyrazolines (4S,5R)-76 (R =Me 87% yield, 99% ee at —40°C) (Scheme 8.18). Simple replacement of the oxazolidinone with the 4,4-dimethyloxazolidinone ring resulted in the formation of (4/ ,5S)-77 (R1 = Me 75% yield, 97% ee at -78 °C). 

The iodine-catalyzed reaction of aziridines with carbon dioxide leads to 2-oxazolidinones (251). Because carbon dioxide effectively polymerizes ethyleneimine, only low yields are obtained when unsubstituted ethyleneimine reacts with C02. However, direct insertion of carbon dioxide [124-58-9] into aziridines can be accomplished, with better yields, by ethoxycarbonylation of aziridines with subsequent elimination of ethylene under flash vacuum conditions (252). 1- Phenyl aziridine [696-18-4] can react with C02 under antimony [7440-56-0] catalysis to give AI-phenyl-2-oxazolidinone in good yields (253). At low temperatures and with the exclusion of atmospheric humidity, the reaction of ethyleneimine with carbon dioxide produces the unstable ethyleneiminium salt [51645-58-2] of IV-vinylcarbamic acid (254,255). 

Diels-Alder reactions of (Z)-A -substituted-4-methylene-5-propylidene-2-oxazoli-dinone dienes with methyl vinyl ketone, methyl propiolate, and captodative alkenes yield the highest regio- and stereo-selectivities in mixtures of H20 and MeOH or under BF3.Et20 catalysis.198 The asymmetric Diels-Alder reaction of cyclopentadiene and 3-acryloyl-2-oxazolidinone is catalysed by a new Cu(II) catalyst containing a chiral sterically congested roofed (2-diphenylphosphino)phenylthiazoline ligand (169).199... 

Seebach, D. Beck, A. K. Badine, D. M. Limbach, M. Eschenmoser, A. Treasury-wala, A. M. Hobi, R. Prikoszovich, W. Linder, B. Are oxazolidinones really unproductive, parasitic species in proline catalysis - Thoughts and experiments pointing to an alternative view, Helv. Chim. Acta 2007, 90, 425-471. 

Substituted oxazolidin-5-one derivatives, which are prepared from N -protected a-annino dicarboxyhc acids and paraformaldehyde, are employed for dual protection of the a-annino and a-carboxy groups in the synthesis of P-aspartyl and y-glutamyl esters (Scheme 4).Py For this purpose the oxazolidinone derivatives are synthesized by treatment of the Z amino acids with paraformaldehyde in a nnixture of acetic anhydride, acetic acid, and traces of thionyl chloride or by azeotropic distillation of the Z amino acids with paraformaldehyde and 4-toluenesulfonic acid in benzene. The resulting heterocychc compounds are readily converted into the tert-butyl esters with isobutene under acid catalysis. Esterification is achieved with tert-butyl bromidet or with Boc-F.P l Finally, the oxazolidinone ring is opened by alkaline hydrolysis or catalytic hydrogenolysis to yield the tert-butyl esters. 

Vinyl oxazolidinone 148 has been shown to be a good precursor to rra r-oxazolines (Scheme 38). Under palladium(O) catalysis, an intermediate 7t-allyl complex is formed with the loss of CO2. Intramolecular attack by the amide oxygen forms the thermodynamically favored /ra r-oxazoline 149. This oxazoline was then converted to the natural product balanol <19990L615>. 

Another standard method for the synthesis of 2-oxazolidinones is by reaction of epoxides with isocyanates. Although 4,5-disubstituted derivatives are not readily accessible by this route, it has been shown that iminodioxolanes (192) add to epoxides in the presence of AICI3 to afford these oxazolidinones in high yield <9lJOC2684>. The reaction proceeds through a spirocyclic intermediate (193) (Scheme 96). The reaction of vinyl epoxides with aryl isocyanates is facilitated by palladium catalysis (Equation (28)) <89TL3893>. The products are obtained by a double inversion process, but... 

Under the catalysis of CuCN/DMEDA (Lll), ynamides could be conveniently synthesized via N-alkynylation of amides, including oxazolidinones, lactams and... 

Oxazolidiaones. Under iodine catalysis, carbon dioxide reacts with aziridines to form 2-oxazolidinones (equation I). In the case of aziridine itself the yield is somewhat low (21.5%) because of polymerization. ... 

Another issue is the formation of oxazolidinones, which has been the subject of study by several research groups and is considered to be part of a parasitic equilibrium for proline-catalysed aldol reactions. More recent studies have indicated that this parasitic equilibrium may not be true, and that reversible oxazolidinone formation may help keep proline in solu-tion. Figure 5.3 illustrates a generalised mechanism for proline catalysis involving enamine intermediates. As aforementioned, the formation of oxazolidinones may or may not be part of a parasitic equilibrium. 

Stereoselective synthesis with carbon dioxide, including preparation of cyclic carbonates, polycarbonates, and oxazolidinone 13ASC2115. Strategies for spiroketal synthesis based on transition metal catalysis ... 

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