L,3-Oxazol-5-one

Aromatic acid chlorides and 2-(triphenylphosphoranylidenamino)cinna-mates (127) give rise to l,3-oxazol-5-ones (129), as shown in Scheme 51. After an intermolecular aza-Wittig reaction with 127, the ethoxy O attacks... 

Anhydro-acylation of l,2-dihydro-2-oxo-l-pyridylacetic acid with acid anhydrides yields bicyclic meso-ionic 4-acyl-l,3-oxazol-5-ones (67). Huisgen and his co-workers have reported extensive studies of the monocyclic meso-ionic l,3-oxazol-5-ones (66), which they have lightheartedly named munchnones. Cyclodehydration of N-benzoyl-A -methyl-C-phenylglycine using acetic anhydride at 55° gives the 3-methyl-2,4-diphenyl derivative (66, R = = Ph R = Me) as... 

V-Benzoyl-C-phenylglycine with trifluoroacetic anhydride at room temperature yields the bright yellow 4-trifluoroacetyl-l,3-oxazol-5-one (66, R = R = Ph R = COCFj), but the corresponding reaction with... 

Ph R = H). Other cyclodehydrating agents used to prepare meso-ionic l,3-oxazol-5-ones (66) include oxalyl chloride or dicyclohexyl-carbodiimide. ... 

Cyclodehydration of l-carboxymethyl-2-pyridone with acetic anhydride and perchloric acid gave the corresponding 1,3-oxazolonium perchlorate which with triethylamine gave the dimer (72) directly. Similar dimerization of other meso-ionic l,3-oxazol-5-ones (66) have been reported. The monomer (71) could not be isolated, but acetyl (67, R = Me) and benzoyl (67, R = Ph) derivatives were prepared from a... 

The meso-ionic 1,3-oxazol-S-ones show an incredible array of cycloaddition reactions. Reference has already been made to the cycloaddition reactions of the derivative 50, which are interpreted as involving cycloaddition to the valence tautomer 51. In addition, an extremely comprehensive study of the 1,3-dipolar cycloaddition reactions of meso-ionic l,3-oxazol-5-ones (66) has been undertaken by Huisgen and his co-workers. The 1,3-dipolarophiles that have been examined include alkenes, alkynes, aldehydes, a-keto esters, a-diketones, thiobenzophenone, thiono esters, carbon oxysulfide, carbon disulfide, nitriles, nitro-, nitroso-, and azo-compounds, and cyclopropane and cyclobutene derivatives. In these reactions the l,3-oxazol-5-ones (66)... 

Two synthetic routes to meso-ionic l,3-diazol-4-ones (91) have recently been reported. 1,3-Cycloaddition of phenyl isocyanate to the meso-ionic l,3-oxazol-5-one (94) yields the intermediate (95 or 96) from which carbon dioxide was extruded in boiling xylene, giving the meso-ionic l,3-diazoi-4-one (97). 

Monocyclic l,3-thiazole-5-thiones (109) are easily prepared by 1,3-dipolar cycloaddition of carbon disulfide to meso-ionic l,3-oxazol-5-ones (66) and l,3-thiazol-5-ones (105). Polycyclic meso-ionic 1,3-thiazole-5-thiones (110) " are formed from carbon disulfide and azomethine ylides (111) derived from isoquinolinium iodides and base. 

The ring fused pyrroles 480 have been prepared by in situ trapping of the meso-ionic l,3-oxazol-5-ones (479) with alkynes. This 1,3-dipolar cycloaddition was found to be regiospecific when phenyl acetylene was used as 1,3-dipolarophile, the only products being 480, R = H or MeO, R = Ph, R2 =... 

Polymers containing pyrrole units have been prepared by the in situ condensation of bis-l,3-oxazol-5-ones with diacetylenes. ... 

In an attempt to investigate this theory further, the analogous alkoxy-substituted nitrile ylides 171 were investigated. Species of this type were previously unknown but were successfully generated for this work by the thermolysis of the 4-alkoxy substituted l,3-oxazol-5-ones 170 (89). In the absence of a dipolarophile, the nitrile ylides reacted via 1,5-electrocyclization to give the isoindoles 173 [see also... 

Solvent-free three-component Biginelli reactions of 2-phenyl-l,3-oxazol-5-one, D-xylose/D-glucose and (thio)ureas 136 in the presence of Ce2(S04)3 salt (10%) under microwave irradiation produced perhydropyrido[l,2-c] pyrimidines 137 and 138 with 94% trans diastereoselectivity (Scheme 3). In the absence of Ce3+ salt no reaction occurred, and without microwave irradiation using conventional heating at 90 °C yields were significantly lower (39-51%) even for longer reaction times (3-5 h). If shorter reaction periods (4-7 min) was applied addition products 139 could be isolated, which then were converted to pyrido[l,2-c]pyrimidines 137 (X = O, R = H) and 138 (X = S, R = Ph) (07SL1905). 

Various other [3 + 2] cycloadditions, affording chiral, anellated C6o derivatives with stereogenic centers in the addends are reported in literature. The products were generally obtained as racemates and resulted from reaction of buckminsterfullerene with species like 2,3-disubstituted 2//-azirincs (via nitrile ylides [under direct irradiation] or via 2-azaallenyl radical cations [sensitization by photoinduced electron transfer]),365 1-substituted 5-diazopentane-1,4-diones (via cyclic carbonyl ylides),366 7-alkylidene-2,3-diazabicyclo[2.2.1] hept-2-ene (via a diradicaloid trimethylenemethane derivative),367 1-benzylpy-razolidine-3-ones in the presence of aldehydes (via pyrazolidinium ylides),368 2-trifluoromethyl-2,5-dihydro-l,3-oxazol-5-ones (via nitrile ylides),369 nitro-alkanes in the presence of triethylamine and trimethylsilyl chloride (via N-silyloxynitrones),370 or dv-HOCH2 CH=C H C H 2 OCO 2 H( in the presence of... 

Among other reactions, the bis-metallated species (151) derived from nitroalkanes condense with dialkyl carbonates to give comp>ounds (152), in 60—80% yield, which can serve as precursors of both a-amino-acids and a-hydroxyamino-esters as well as a-keto-esters. Oxazolin-5-ones (153) can be alkylated at the 4-position by alkyl halides in hot DMF containing HMPA and ethyldi-isopropylamine. Yields are good (60—90%) for allylic, benzylic, and propargylic halides but otherwise poor (e.g. 32% with EtI) under these conditions acid hydrolysis of the products affords substituted a-amino-acids. Mesoionic l,3-oxazol-5-ones (154), obtained from imidoyl chlorides and acyl-tetracarbonylferrates, react with alcohols to give N-acyl-a-amino-acid esters. ... 

Diaryl or arylalkyl imidoyl chlorides react with the acyltetracarbonylferrate anions (67) at room temperature in CH2CI2 to give the mesoionic l,3-oxazol-5-ones (68) in isolated yields of 37—65%. The anion (67) is generated in the normal way by reaction of [Fe(CO)s] with sodium amalgam followed by reaction with the appropriate acid chloride at -30 °C. The mesoionic compounds (68) are useful intermediates since they react with alcohols to give a-amino-acids and undergo a variety of cycloaddition reactions to form new heterocycles. 

A mixture of 2-phenyl-l,3-oxazol-5-one (1,2.0 mmol), tosylaziridine 2 (2.0 mmol), and a catalytic amount of I2 (0.2 mmol) in [bmim]OH (5 mL) was stirred at room temperature for 5-6 h. After completion of the reaction as indicated by TLC, distilled water (10 mL) was added, and the mixture was extracted thrice with ethyl acetate (10 mL). The combined organic layer was washed with brine (10 mL), dried over anhyd. Sodium sulfate, filtered, and evaporated under reduced pressure to obtain pure diastereoselectively pure product of pyrrolidine-2-one 3 in excellent yield. The remaining aqueous layer containing the ionic liquid was washed with hexane and dried in vacuum resulting in recycled ionic liquid, [bmim]OH and reused. Each of the products 3 was characterized on the basis of detailed spectral as well as elemental analyses. 

Typical examples of oxazoline monomers to be polymerized via CROP mode are shown in Scheme 3. Not only five-mem-bered monomers of ROZO and 5-oxazolones (4,5-dihydro-l,3-oxazol-5-one, ROZLO) but also six-membered analogs (5,6-dihydro-4H-l,3-oxazines, ROZI) and seven-membered ones (4,5,6,7-tetrahydro-4H-l,3-oxazepine, ROXP) have been polymerized. 2-Iminotetrahydrofurans (ITHFs) are known as an exo-cydic imino ether derivative of ROZO. CROP of ITHF was reported in 1963, which was preceded by the studies on the CROP of OZOs. Preparations of these monomers have been well known and documented. ... 

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