1.3- Oxazolidines

Although the synthesis of the oxazolidinone 159 appeared to be well established, the scale-up of the reaction gave poorly reproducible results. The synthesis was much more efficient using diphosgene and a catalytic amount of activated charcoal 06S885 . 

Another synthesis of 5-methylene-l,3-oxazolidin-3-ones can be achieved using Au(I) to catalyze the cyclization of A-propargyl carbamates 160. The reaction proceeds under very mild conditions and was applied to a large number of compounds 06SL2727 . 

A high degree of selectivity can be obtained in the base catalysed epimerization of 1,3-oxazolidin-2-ones 166 and 167. Through a proper choice of the base and substituents a selectivity up to 99 1 can be obtained for both the trans and cis isomers 06JOC5008 . 

Some reactions in which a preformed 1,3-oxazolidine ring is transformed into another oxazolidine derivative were described. A detailed study of the enantioselective reduction of A-tosyl-4-alkylidene-l,3-oxazolidin-2-ones under the catalysis of Rh salts and chiral ligands, was published 06T9237 . 

Three sets of oligomers containing the 4-carboxy-5-methyloxazolidin-2-one moiety, one example is compound 170, were synthesized with the aim of verifying if these systems are able to give a (i-bend ribbon spiral 06JA2410 . 

A practical gold-catalyzed route to 4-substituted oxazolidin-2-ones 160 has been described. This synthesis starts from JV-Boc propargylamines 158. This route was applied to both terminal and internal triple bonds although the latter react much more slowly 07EJ03503 . 

In a different approach, the synthesis of oxazolidin-2-one was accomplished by reaction of P-amino alcohols, like 168, with urea under microwave irradiation in a minimal amount of a polar solvent like nitromethane 07S3111 . 

Another possible synthesis is offered by the reaction of alkoxy- or aryloxysulfonylisocyanate to epichloridrine derivatives. The intermediate carbamate easily cyclises upon heating in acetone 07SC2215 . Alternatively phenyl 2-hydroxyalkyl selenides can react with benzoyl isocyanate and the final carbamate cyclize after oxidation of the selenyl functionality 07SC2693 . 

Several examples appeared in the literature describing the use of oxazolidin-2-ones as chiral auxiliaries or being involved in directing the stereoselectivity of a reaction 07CEJ1842 07EJO5487 07OL211 07S669 . 

The reaction of a halomethyloxirane, like 175, with benzylamine 176 in the presence of K2CO3 and NEts afforded the fV-benzyl oxazolidin-2-one 178 very efficiently. A careftil analysis of the reaction demonstrated that the final product was obtained through the ring contraction of the intermediate oxazinone 177 which was unstable in the reaction conditions 05JOC5737 . 

A modified Mg Al hydrotalcite was revealed as an excellent catalyst for the conversion of a-hydroxy carbamates into the corresponding oxazolidin-2-ones. The reaction is performed in refluxing toluene affording the expected products in high yields (83-96%, 6 examples) 05OBC967 . 

Two detailed procedures for the practical preparation of chiral allenamide 179 0508147 and oxazolidin-2-one 180 0508112 were published. Transformation of a-amino acids, like proline 181, into substituted allylic alcohols allowed a highly stereoselective 8n2 cyclization affording enantiopure oxazolidin-2-ones, like 183 bearing a vinyl group on C-5. This procedure was applied to a series of amino acids with good yields and selectivity 

Particularly significant is the extension to the S5mthesis of enantioenriched oxazolidin-2-thiones of the reaction of isothiocyanate 189 with aromatic aldehydes. This reaction is catalysed by Mg(C104) and the asymmetric induction is provided by a pybox ligand 05AG(E)1543 . A different approach to enantioenriched oxazolidin-2-thione was provided by a kinetic resolution of racemic substrate with an organic catalyst. Compound 192 efficiently catalysed the methanolysis of iV-acyl oxazolidinethiones 191 and afforded an efficient kinetic resolution of 191 with an s-factor up to 32 05JA13502 . 

A -Acyl-oxazolidin-2-ones, as 203, are widely used in aldol reactions, however an unprecedented use of the aldol adducts for a stereoselective synthesis of trisubstituted a, 3-unsaturated amides and acids was reported. The yy -aldol adduct 204 underwent clean elimination upon treatment with KHMDS and afforded the E -olefin 205 with a 97% ds. The reaction was wide in scope but with a loss in selectivity using a,P-unsaturated or chiral aldehydes 05OBC2976 . This synthetic approach found immediate application in the synthesis of semiplenamide C 206 05TL5547 . Oxazolidin-2,4-diones 207, obtained from cyanohydrins, can be easily converted into the corresponding a-hydroxyamides 208 in a reaction that can be accelerated by microwaves 05T7247 . 

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Intramolecular reaction of the allenyl carbamate 5 in the presence of a large excess of allylic chloride catalyzed by Pdi(dba)3 or PdCl2(PhCN)2 affords the substituted oxazolidin-2-one 6. Since the reaction is catalyzed by both Pd(II) and Pd(0), its mechanism is not dear[3]. 

Thermolysis of the aziridine (446) in the presence of diphenylketene gave a mixture of the pyrrolidone (447 minor product) and the oxazolidine (448 major product). In this instance the preferential addition to the C=0 bond is explained in terms of steric effects (72CC199). Similar addition to diphenylacetaldehyde takes place with the same orientation and the oxazolidine (448a) was obtained. When the reaction of the aziridine with the aldehyde was carried out in the presence of hydrogen selenide a selenazolidine was obtained (72BSB295). 

Aroylaziridines (32) and aromatic aldehydes react to give oxazolidines (33), the stereochemistry of which suggests reaction very largely through the trans-azomethine ylide, irrespective of the aziridine configuration (70JCS(C)2383). 

Oxazolidine, cis-4-methyl-5-phenyl- C NMR, S, 20 (79MI40100) Oxazolidine-2-thione IR, S, 26 (63PMH(2)161)... 

Oxazolidine-4,5-dione, At-benzoyl-synthesis, 6, 231 Oxazolidinediones reactions, 6, 214 structure, 6, 179 Oxazolidine-2,4-diones as anticonvulsants, 1, 166 NMI 6, 181 reactions, 6, 214 s mthesis, 6, 231 OxazoIidine-2,5-diones crystal structure, 6, 185 reactions, 6, 214 polymers, 1, 307 s mthesis, 6, 231 Oxazolidine-4,5-diones synthesis, 6, 231 Oxazolidines... 

Oxazolidin-5-one, bis(trifluoromethyl)-reactions, 6, 213 Oxazolidinones polymers, 1, 281-282 reactions, 6, 213 Oxazolidinones, imino-rearrangement, 5, 775 Oxazolidinones, vinyl-polymers, 1, 281 Oxazolidin-2-ones circular dichroism, 6, 185 H NMR, 6, 181 IR spectroscopy, 6, 183 PE spectroscopy, 6, 183 reactions, 6, 213... 

Pyrrolidino[l,2-6][l,3,4]oxadiazoline, 5-phenyl-biological activity, 6, 1024 Pyrrolidino[2,1 -6][1,3]oxazolidines synthesis, 5, 137 Pyrrolidino[l,2-6]pyrazolines synthesis, 5, 148... 

LiBF4, wet CH3CN, 96% yield.Unsubstituted 1,3-dioxolanes are hydrolyzed only slowly, but substituted dioxolanes are completely stable.This reagent proved excellent for hydrolysis of the dimethyl ketal in the presence of the acid-sensitive oxazolidine. ... 

An oxazolidine was used to protect the carbonyl group in an a,/3-unsaturated aldehyde during reduction of the carbon-carbon double bond by H2/Raney Ni. It... 

Oxazolidines are prepared to allow selective protection of the ct- or aj-C02H groups in aspartic and glutamic acids. 

Several blocked diamines or amino-alcohols are commercially available. The aldimine is an aldehyde-blocked diamine. The ketimine is a ketone-blocked diamine. The oxazolidine is a five-membered ring containing oxygen and nitrogen. The oxazolidine ring shown below is an aldehyde-blocked amino alcohol. The basic synthetic concepts of an aldimine, a ketimine, and an oxazolidine are shown below ... 

The 2,2-bis(tnfluoromethyl)-4-methyl-2f/-5-oxazolone, readily available from 2,2-bis(trifluoromethyl)-l,3-oxazolidin-5-one, is a synthetic equivalent of activated pyruvate [90] (equation 16). 

Similarly, trimethylsilyl inflate can be used as a catalyst for the alkylation of 2 methoxy 1,3-oxazolidines [104] or 1-acetoxyadamantane [105] with allylsilane and for the reduction of acetals to ethers with trialkylsilanes [106]... 

The previous sections have dealt with stable C=N-I- functionality in aromatic rings as simple salts. Another class of iminium salt reactions can be found where the iminium salt is only an intermediate. The purpose of this section is to point out these reactions even though they do not show any striking differences in their reactivity from stable iminium salts. Such intermediates arise from a-chloroamines (133-135), isomerization of oxazolidines (136), reduction of a-aminoketones by the Clemmensen method (137-139), reductive alkylation by the Leuckart-Wallach (140-141) or Clarke-Eschweiler reaction (142), mercuric acetate oxidation of amines (46,93), and in reactions such as ketene with enamines (143). 

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