Oxazolidines, reactions

The second method consists of the reaction of melamine with oxazolidine (reaction 15.39) [31]. 

Unfortunately, due to the low solubility of melamine in oxazolidine, reaction 15.39 takes place slowly, needs a long reaction time and unreacted melamine frequently remains. The best method for the synthesis of melamine Mannich base is the Mannich reaction in the presence of aqueous formaldehyde. 

By proper selection of the radicals Rj and R2t the rate of the Isocyanate-oxazolidine reaction can be made much faster than that of the hydrolysis reaction of the Isocyanate alone. 

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-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... 

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). 

Diastereomeric oxazolidines 88 and 89 (Scheme 8.4.27) were available via 1,4-reduction and cyclization of Zincke product 87, with 88 being the kinetic product under the reaction conditions and 89 (X-ray) the thermodynamically favored isomer in CDCI3 solution. Iterative reductive oxazolidine opening provided 3-aryl piperidine 91, which was readily advanced to (-)-PPP (92), a selective dopaminergic receptor antagonist. ... 

However, when carrying out the synthetic route, as shown below, isoquinoline production was not realized. Rather, the oxazolidine intermediate (27) was isolated. Fortunately, an X-ray of the intermediate was obtained that proved unambiguously, that 2-oxazolidines were an intermediate in the Pictet-Gams reaction. 

A variety of 1,3-oxazolidines have been used as chiral formyl anion equivalents for addition to aldehydes. Thus, for example, reaction of N-protected norephedrine with Bu3Sn-CH(OEt)2 gives 48, and transmetallation with BuLi followed by addition of benzaldehyde affords the expected adduct 49. The selectivity at the newly formed alcohol center is poor, but the situation can be salvaged by oxidation and re-reduction, which affords the product 50 with >95% d.e. It is then a simple matter to hydrolyze off the oxazolidine, although the resulting hydroxyaldehydes... 

The Asymmetric Diels-Alder Reaction of 3-Alkenoyl-l,3-oxazolidin-2-ones as Dienophile... 

Chiral 3-alkenoyl-l,3-oxazolidin-2-ones have been developed and used in highly diastereoselective Diels-Alder reactions by Evans et al. [26] (Scheme 1.34). In this reaction these dienophiles are highly reactive compared with the corresponding... 

A chiral titanium complex with 3-cinnamoyl-l,3-oxazolidin-2-one was isolated by Jagensen et al. from a mixture of TiCl 2(0-i-Pr)2 with (2R,31 )-2,3-0-isopropyli-dene-l,l,4,4-tetraphenyl-l,2,3,4-butanetetrol, which is an isopropylidene acetal analog of Narasaka s TADDOL [48]. The structure of this complex was determined by X-ray structure analysis. It has the isopropylidene diol and the cinnamoyloxazolidi-none in the equatorial plane, with the two chloride ligands in apical (trans) position as depicted in the structure A, It seems from this structure that a pseudo-axial phenyl group of the chiral ligand seems to block one face of the coordinated cinnamoyloxazolidinone. On the other hand, after an NMR study of the complex in solution, Di Mare et al, and Seebach et al, reported that the above trans di-chloro complex A is a major component in the solution but went on to propose another minor complex B, with the two chlorides cis to each other, as the most reactive intermediate in this chiral titanium-catalyzed reaction [41b, 49], It has not yet been clearly confirmed whether or not the trans and/or the cis complex are real reactive intermediates (Scheme 1.60). 

Among the many chiral Lewis acid catalysts described so far, not many practical catalysts meet these criteria. For a,/ -unsaturated aldehydes, Corey s tryptophan-derived borane catalyst 4, and Yamamoto s CBA and BLA catalysts 3, 7, and 8 are excellent. Narasaka s chiral titanium catalyst 31 and Evans s chiral copper catalyst 24 are outstanding chiral Lewis acid catalysts of the reaction of 3-alkenoyl-l,2-oxazolidin-2-one as dienophile. These chiral Lewis acid catalysts have wide scope and generality compared with the others, as shown in their application to natural product syntheses. They are, however, still not perfect catalysts. We need to continue the endeavor to seek better catalysts which are more reactive, more selective, and have wider applicability. 

To achieve catalytic enantioselective aza Diels-Alder reactions, choice of metal is very important. It has been shown that lanthanide triflates are excellent catalysts for achiral aza Diels-Alder reactions [5]. Although stoichiometric amounts of Lewis acids are often required, a small amount of the triflate effectively catalyzes the reactions. On the basis of these findings chiral lanthanides were used in catalytic asymmetric aza Diels-Alder reactions. The chiral lanthanide Lewis acids were first developed to realize highly enantioselective Diels-Alder reactions of 2-oxazolidin-l-one with dienes [6]. 

A frequently used catalytic system used for the catalytic enantioselective carbo-Diels-Alder reaction of N-alkenoyl-l,3-oxazolidin-2-one 4 is the chiral TADDOL-Ti(IV) 6 [14] complexes (Scheme 8.2 see Ghapter 1 in this book, by Hayashi) [15]. 

El fazepam (80) not only is a tranquilizer, but also stimulates feeding in satiated animals. One of several syntheses involves reaction of benzophenone derivative with a glycine equivalent masked as an oxazolidine-2,5-dione (79). ... 

The related serine derived (4S)-4-methoxycarbonyl-3-(l-oxopropyl)-2-thiono-l,3-oxazolidine 11, and the cysteine derived (4A)-4-methoxycarbonyl-3-(l-oxobntyl)-2-thiono-1,3-thiazolidine 13, also serve as efficient chiral auxiliaries in boron- and tin(II)-mediated aldol condensations98. Thus, conversion of 11 into the boron or tin enolate, followed by reaction with 2-methylpropanal affords predominantly one adduct. Subsequent methanolysis and chromatographic purification delivers the syu-methyl ester in 98% ee. 

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