Oxazoles esters

DBU (3mL, 20 mmol) was added to methyl 2-[(benzyloxycarbonylamino)oxazolidine-4-carboxylate (2.8 g, 9.6 mmol) in CQ4/MeCN/Py (2 3 3). After 3 h at rt, the solvent was extracted with 0.5 M HC1 and the aqueous phase reextracted with EtOAc (2 x). The EtOAc phase was washed with brine, dried (MgS04), and the solvent removed. Chromatography (silica gel, EtOAc/hexane 1 1) afforded methyl 2-[(benzyloxycarbonylamino)methyl]oxazole-4-carboxylate yield 0.94 g (33%). The oxazole ester (0.29 g, lmmol) was dissolved in dioxane (15 mL) and NaOH (0.12 g, in 5mL H,0) was added. The mixture was stirred at rt for 1 hr. The soln was neutralized with 10% aq KHS04 to pH 6, and the dioxane was removed. The soln was acidified to pH 3 and taken to dryness. The residue was crystallized (EtOAc/ hexane) yield 0.24 g (90%). 

Quinones, thiazoles, oxazoles Esters, carbonyl compounds, sulfide derivatives, carbinols Same as methyl acetate... 

Commencing with oxazole 66 generated in two steps from oxazole ester derivative 68, deprotonation of 66 followed by quenching with isatin derivative 67 provided tertiary alcohol 69 in 73% yield. Refluxing 69 with phenol 65 in the... 

Oxazoles with an acyl substituent at C4 can undergo a thermal rearrangement essentially exchanging the C4 and C5 substituents. The facility of this rearrangement is improved when the C5 substituent is a heteroatom (-OR, -SR, -Cl). Dewar and Turchi observed deuterium scrambling of a labelled oxazole ester under thermal conditions. They propose a nitrile ylide intermediate in the rearrangement mechanism. This... 

To a mixture of 0.15 g selenol ester (0.41 mmol), 63 mg triethylamine (0.62 mmol), and 0.12 g methyl isocyanoacetate (1.21 mmol) in 5 mL anhydrous THF was added 92 mg anhydrous cuprous oxide (0.62 mmol). After being stirred at room temperature for 1 h, the reaction mixture was filtered through a pad of silica gel, which was eluted with EtOAc. The combined filtrate was concentrated in vacuo and the residue was purified by flash chromatography using EtOAc/hexane (1 3) as the eluent to afford 0.11 g oxazole ester as a colorless oil, in a yield of 73%. 

A large variety of newer poly(ether imide)s has been described. Included among these are perfluorinated polymers (96), poly(ester ether imide)s (97), poly(ether imide)s derived from A/,Ar-diamino-l,4,5,8-naphthalenetetracarboxyHcbisimide (98), and poly(arylene ether imide ketone)s (99). In addition, many other heterocyHc groups have been introduced into polyether systems, eg, poly(pyrazole ether)s (100) and poly(aryl ether phenylquinoxaLine)s (101) poly(aryl ether oxazole)s with trifluoromethyl groups (102) and polyethers with other heterolinkages, eg, poly(arylether azine)s (103). 

Decomposition of the diazoacetic ester (548) to the keto carbene (549) is promoted by copper(II) trifluoromethanesulfonate. In the presence of nitriles, 1,3-dipolar addition to the nitrile occurred giving the oxazole (550) (75JOM(88)ll5) (see also Section 4.03.8.1). 

The isoxazole (19a) when photolyzed produced two oxazoles (20) and (21) which were not interconvertable under the reaction conditions. The corresponding esters (19b) and (19c) gave (20b) and (20c), respectively. These studies were instrumental in establishing the photointerconversion of 4- and 5-acylisoxazoles (76HCA2074). 

They found that deuterium labeled 2-phenyl-5-methoxy-4-[(methoxy-d3)-carbonyl]oxazole (7) scrambled on heating to give a 1 1 equilibrium mixture of 7 and the corresponding rearranged ester 9 ... 

In 1972, van Leusen, Hoogenboom and Siderius introduced the utility of TosMIC for the synthesis of azoles (pyrroles, oxazoles, imidazoles, thiazoles, etc.) by delivering a C-N-C fragment to polarized double bonds. In addition to the synthesis of 5-phenyloxazole, they also described reaction of TosMIC with /7-nitro- and /7-chloro-benzaldehyde (3) to provide analogous oxazoles 4 in 91% and 57% yield, respectively. Reaction of TosMIC with acid chlorides, anhydrides, or esters leads to oxazoles in which the tosyl group is retained. For example, reaction of acetic anhydride and TosMIC furnish oxazole 5 in 73% yield. ... 

Van Leusen and co-workers also demonstrated the utility of dilithio-tosylmethyl isocyanide (dilithio-TosMIC) to extend the scope of the application. Dilithio-TosMIC is readily formed from TosMIC and two equivalents of n-butyllithium (BuLi) in THF at -70"C. Dilithio-TosMIC converts ethyl benzoate to oxazole 14 in 70% yield whereas TosMIC monoanion does not react. In addition, unsaturated, conjugated esters (15) react with dilithio-TosMIC exclusively through the ester carbonyl to provide oxazoles (16). On the other hand, use of the softer TosMIC-monoanion provides pyrroles through reaction of the carbon-carbon double bond in the Michael acceptor. 

TosMIC reagents. For example, glyoxylic acid ethyl ester undergoes cycloaddition with (2-naphthyl) tosylmethyl isonitrile (17) to produce oxazole 18 in good yield. ... 

An example of this methodology was its use in the synthesis of vitamin Be, pyridoxine 12. Cycloaddition of oxazole 9, prepared from ethyl A-acetylalanate and P2O5, with maleic anhydride initially gave 10. Upon exposure to acidic ethanol, the oxabicyclooctane system fragments to afford pyridine 11. Reduction of the ester substituents with LiAlIU generated the desired product 12. 

The diazotization of heteroaromatic amines is basically analogous to that of aromatic amines. Among the five-membered systems the amino-azoles (pyrroles, diazoles, triazoles, tetrazoles, oxazoles, isooxazoles, thia-, selena-, and dithiazoles) have all been diazotized. In general, diazotization in dilute mineral acid is possible, but diazotization in concentrated sulfuric acid (nitrosylsulfuric acid, see Sec. 2.2) or in organic solvents using an ester of nitrous acid (ethyl or isopentyl nitrite) is often preferable. Amino derivatives of aromatic heterocycles without ring nitrogen (furan and thiophene) can also be diazotized. 

C22H2XO3 14135-32-1) see Betamethasone 17a-hydroxy-16P-methyl-5p-pregn-9(ll)-ene-3,20-dione (C22H32O3 13656-78-5) see Betamethasone 21-hydroxy-2 -methyl-5p//-5a-pregn-9(ll)-eno[17,16-d]-oxazole-3,20-dione acetate (ester)... 

The mechanism of the condensation in Part D probably involves thioformylation of the metallated isocyanoacetate followed by intramolecular 1,1-addition of the tautomeric enethiol to the isonitrile. This thi2izole synthesis is analogous to the formation of oxazoles from acylation of metallated isonitriles with acid chlorides or anhydrides. " Interestingly, ethyl formate does not react with isocyanoacetate under the conditions of this procedure. Ethyl and methyl isocyanoacetate have been prepared in a similar manner by dehydration of the corresponding N-formylglycine esters with phosgene and trichloromethyl chloroformate, respectively. The phosphoryl chloride method described here was provided to the submitters by Professor U. Schollkopf and is based on the procedure of Bohme and Fuchs. The preparation of O-ethyl thioformate in Part C was developed from a report by Ohno, Koi/.uma, and Tsuchihaski. " ... 

The N-silylated enol acetate 1523 is cyclized by TMSOTf 20 in CHCI3, in 95% yield, giving the oxazole 1524 [57]. The dimeric derivative 1525 affords the 2,2 -bis-oxazole 1526 in 46% yield [57]. 2-Benzoylamino-3-chloropyridine 1527 is cyclized by polyphosphoric acid trimethylsilyl ester (PPSE) 195 on heating for 15 h in boiling 1,2-dichlorobenzene to give 40-60% 2-phenyloxazolo[5,4-f)]pyridine 1528 [58] (Scheme 9.34). 

Application of the Ritter reaction conditions on y-hydroxy-a,P-alkynoic esters, 102, produced ethyl 5-oxazoleacetates 103 or y-A-acylamino-P-keto ester 104 by reaction with aryl or alkyl nitriles respectively. The y-A-acylamino-P-keto ester 104 can also be transformed into oxazole derivatives using an additional step involving POCI3 <06TL4385>. 

When l-[diazo(methoxycarbonyl)acetyl]-2-oxopyrrolidine derivative 231 was treated with Rh2(pfm)4 (pfm = per-fluorobutyro amidate) in the presence of W-phenylmaleimide, none of the desired dipolar cycloadduct was formed but instead the acidic proton at C-3 in the isomiinchnone intermediate 232 was transferred, and the fused oxazoli-dinone 3-oxo-2,3,5,6-tetrahydropyrrolo[2,l- ]oxazole-2,7-dicarboxylic acid dimethyl ester 233 was isolated in 77% yield (Scheme 33) <1997JOC6842>. 

The Michael addition reaction of the serine-derived oxazolidine 326 with ethyl acrylate gave two products. The major product of the reaction was found to be the bicyclic compound 327, which was formed in 27% yield, accompanied by the unsaturated ester 328. The Dess-Martin oxidation of 327 resulted only in formation of the elimination product, the 7,7a-dihydro-177, 377-pyrrolo[l,2-r ]oxazole 328 (Scheme 46) <2001JOC7555>. 

The first syntheses of a-allenic a-amino acids [131,133] took advantage of Steg-lich s [134] protocol for the oxazole-Claisen rearrangement of unsaturated N-ben-zoylamino acid esters (Scheme 18.46). Thus, treatment of the propargylic ester 143 with triphenylphosphine and tetrachlormethane furnished the allenic oxazolone 144, which was converted into the amino acid derivative 145 by methanolysis. Stepwise deprotection finally led to the allenic DOPA analog 146, which shows a much higher decarboxylase-inhibiting activity than a-vinyl- and a-ethynyl-DOPA [133],... 

F Weygand, W Steglich, X Boracio de la Lama. On the sterical course of the reaction of oxazol-5-ones with amino-acid esters. Tetrahedron Suppl 8, part 1, 9, 1966. 

In a similar way, carboxylic esters have been obtained stoichiometrically by ortho palladation of aromatic amides (Scheme 25) [147] and of phenyl-substituted isoxazoles or oxazoles [148] followed by alkoxycarbonylation. 

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