Oxazoli dines

Figure 3, Structures of oxygen-containing cyclic nitrosamines nitrosomorpholine, 2-methylnitrosomorpholine, 2,6-dimethylnitrosomorpholine, nitroso-1,3-oxazoli-dine, 5-methylnitroso-l,3-oxazolidine, 2-methylnitroso-l,3-oxazolidine, nitrosotet-...

Another type of spin traps, which have been recommended for the detection of superoxide, are the derivatives of hydroxylamine. In 1982, Rosen et al. [25] showed that superoxide is able to oxidize the hydroxylamine derivative 2-ethyl-1-hydroxy-2,5,5-trimethyl-3-oxazoli-dine (OXANOH) to corresponding free radical 2-ethyl-1-hydroxy-2,5,5-trimethyl-3-oxazolidinoxyl (OXANO). Although this radical is very stable and easily identified by its ESR spectrum, it is also easily reduced by ascorbic acid and other reductants. Furthermore, OXANOH and other hydroxylamines are oxidized by dioxygen in the presence of transition metal ions to form superoxide, and therefore, superoxide detection must be carried out in the presence of chelators. 

Davies and colleagues266 studied the use of copper(II) complexes of chiral bis(oxazoli-dine) 430 as catalysts in the cycloadditions of cyclopentadiene to substituted /V-acryloyl-l,3-oxazolidin-2-ones. They observed high endo and enantioselectivities. Again, the highest enantioselectivities were observed using SbEfi as the counterion, although differences were small this time ee values of 92 and 95% were obtained for the triflate and S h I Y> based catalysts, respectively. 

Husson and co-workers (84) investigated the 1,3-dipolar cycloaddition of acyclic chiral azomethine ylides derived from (—)-Af-cyanomethyl-4-phenyl-l,3-oxazoli-dine with electron-deficient alkenes, and in some cases de >95% were obtained. 

Fig. 17.7. This figure illustrates the advantages and disadvantages of using partitioning. On the one hand, the timings (shown next to the individual points in seconds) are tremendously reduced, on the other hand the effectiveness of the optimized oxazoli-dine library is sub-optimal with smaller partitions. A partition of 16 reagents seems best overall.

Keywords aldehyde, (-)-ephedrine, (-t-)-pseudoephedrine, optically activ oxazoli-dine... 

Methyloxalyl chloride reacts with cyclic carbodiimides (n = 6) to form the spirobi(oxazoli-dine) derivative 59. ... 

When amidals obtained from secondary allylic alcohols are cyclized with mercury(ll) acetate or mercury(II) acetate and trifluoroacetic acid, the corresponding 4,5-disubstituted oxazoli-dines 12 and 13 are formed. The 1,3-asymmetric induction overrides the competing 1,2-asymmet-ric induction of the allylic substituent. When the tram-isomers 12 were formed, only one diastereomer was obtained. However, when steric interactions between the substituents are low, m-diastereomers were predominantly obtained, e.g., 13, although the amount of the nans-diastereomcrs increases on increasing the bulkiness of the allylic substituent. As the oxazolid-ines obtained by mercury-induced cyclization of the amidals are easily cleaved to amino alcohols with hydrazine, this approach allows either a syn- or vicinal amino alcohol to be obtained starting from a single secondary allylic alcohol. 

Related a,p-Unsaturated Esters. Similar a,p-unsaturated esters bearing a heterocyclic chiral auxiliary of a-amino acid origin at the p-position are known and have been utilized in asymmetric synthesis. Effective asymmetric conjugate additions of cuprates to (2), (3), and (5)J epoxidations of (3), and dipolar cycloadditions of (2) have been reported. Although oxazoli-dine (4) is only obtained as an 86 14 equilibrating mixture of stereoisomers, reactions with the lithium (Z)-enolate of methyl N-benzylideneglycinate (see Ethyl N-Benzylideneglycinate) are exclusively diastereoselective. 

Another route for the synthesis of 3-oxazolines is via a chlorination/dehydrochlorination sequence of 1,3-oxazoli-dines, for example, 268 <2000TL9787>. This net oxidation reaction results in mixtures of 2- and 3-oxazolines (269 and 270, respectively) with the product ratios dependent on the nature of the base used (Equation 14). 

Chien DS, Schoenwald RD. Ocular pharmacokinetics and pharmacodynamics of phenylephrine and phenylephrine oxazoli-dine in rabbit eyes. Pharm Res 1990 7 476-483. 

The three-component reaction of N-benzylidenemethylamine with phe-nyldiazomethane and benzaldehyde proceeds via an azomethine ylide, which is stabilized by 1,3-dipolar addition to an aldehyde, furnishing oxazoli-dine 551 (84T2569). 

As depicted in Scheme 4, oxazinanes 31 (R = Ph, Me, CH2COOEt) and oxazoli-dine 30 (R = CH2COPh) react with 1,3-cyclohexanediones 61 (R1 = Me, H) to form the corresponding 1 2 stoichiometric products 62 and xanthene derivatives 63. However, 30 (R = CH2COCH2COMe/OEt, in similar reactions form functionalized a-tetralones 64a-c. Acyclic carbon nucleophiles, such as ethyl acetoacetate, mal-ononitrile, nitromethane, dibenzoylmethane, and diethyl malonate, react with 31 (R = Ph) in the presence of an acid to form the corresponding styrene derivatives 65 (X = MeCO, CN, N02, COPh, COOEt Y = COOEt, CN, H, COPh, COOEt) only. 

Bashiardes et al. [94] described an intramolecular cydoaddition reaction of unprotected carbohydrates 126, involving a nitrone ylide dipole 127 derived from the 1-aldehydic position, and an co-olefinic moiety constructed from the 6-hydroxyl function (Scheme 11.32). In this enantiomeric synthesis of novel bicyclic oxazoli-dines bearing a quaternary bridgehead, 128, a comparative study was performed of classical heating conditions and microwave-assisted cydoaddition, both in the same reaction medium, aqueous ethanol. All the examples provided products in yields which were improved from approximately 60% to 90%, basically because of the cleaner reactions. The reaction times were reduced from 48 h to just 1 h. 

Shreeve et al. have synthesized a range of new ionic liquids based on oxazoli-dine, morpholine and 1,2,4-triazole. These have been found to be good solvents for the Cu(I)-mediated nucleophilic trifluoromethylation of benzyl bromide [155]. Nucleophilic substitution has also been carried out on alkenes in the form of 2-tosyltropone, where the tosyl group was substituted for a chloride in [BMIM][BF4] [156]. Aminopyridines [157] and aminopyrimidines [158] react with a-halo ketones to form imidazopyridines and imidazopyrimidines. These reactions have been investigated in [Bp4] and [PFs]" ionic liquids and found to give fester reaction rates than in organic solvents [159]. 

Other 3-aiyl aminopropanoic acid derivatives have been prepared using oxazoli dine derivatives derived from vinyl acetates and hydroxylamines.62 Nitrone 2.126 is more sterically encumbered than the nitrones shown previously, and reaction with vinyl acetate gave a poor yield of 2.727.62 Hydrolysis of 2.337, followed by oxidation and catalytic hydrogenation led to 4-methyl-3-aminopentanoic acid, 2.128. ... 

Regulatory Canada DSL Trade Names Alkaterge -T Oxazolidine A. See Dimethyl oxazolidine Oxazoline deriv., ethoxylated. See 2,2 [(2-Heptadecyl-4(5H)-oxazoli-dine)bis(methyleneoxy-2,1-ethanediyloxy)]bi-s-ethanol... 

Mutter and coworkers introduced pseudoprolines, which are Ser or Thr oxazolidines (N and O of the Ser or Thr residue) [60]. They are incorporated as the dipeptides, e.g., Gly-Ser. The oxazoli-dine ring can be opened with TFA-containing cocktails to unprotect the peptides. 

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