5 -Oxazolones oxidation

Oxidative dimerization of various 2-benzyloxy-2-thiazoline-5-ones (222) catalyzed by iodine and triethylamine is another example of the nucleophilic reactivity of the C-4 atom (469) (Scheme 112). Treatment of 212 with pyrrolidinocyclohexene yields the amide (223) (Scheme 113). The mechanism given for the formation of 223 is proposed by analogy with the reactivitx of oxazolones with enamines (4701. 4-Substituted 2-phenylthiazol-5(4Hi-ones react with A -morphoiino-l-cyclohexene in a similar manner (562j. Recently. Barret and Walker have studied the Michael addition products... 

Diazoalkanes add to the carbon-carbon double bonds of 2,3-diphenylthiirene 1-oxide and 1,1-dioxide. The adducts lose SO or SO2 to give pyrazoles and related compounds (Scheme 103) (80CB1632). Mesoionic oxazolones (75CLH53), 4-methyl-5-phenyl-l,2-dithiolene-3-thione (80JOU395) and pyrylium betaines (72JOC3838) react similarly via intermediate adducts (Scheme 104). Enamines (Scheme 96) and ynamines add to the double bond of 2,3-diarylthiirene 1,1-dioxides to give acyclic and cyclic sulfones by a thermal. 

Ortho esters, in synthesis of symmetrical trimethine thiazolocyanines, 54 Oxazolone, for neutrocyanines, 27 Oxidation potentials, of dyes, 75 of mesosubstituted dyes, in relation with absorption, 77 of polymethine dyes, 72 Oxidoreduction, relation between sensitizers, and silver halides, 78 4-Oxo-disubstituted 2-aminoselenazoles, table of products, 262 Oxonols, nomenclature of, 26 in synthesis of dimethine neutrocyanines, 62... 

The two overwhelming oxidation products of the purine moiety of dGuo 37 arising from the transformation of guanine radical cations 38 were isolated and identified as 2,2-diamino-4-[(2-deoxy-/l-D-eryfhro-pentofura-nosyl)amino]-5(2H)-oxazolone (41) and its precursor 2-amino-5-[(2-deoxy-... 

Several approaches to the 1,2,3-triazole core have been published in 2000. Iodobenzene diacetate-mediated oxidation of hydrazones 152 led to fused 1,2,3-triazoloheterocycles 153 <00SC417>. Treatment of oxazolone 154 with iso-pentyl nitrite in the presence of acetic acid gave 1,2,3-triazole 155, a precursor to 3-(W-l,2,3-triazolyl)-substituted a,P-unsaturated a amino acid derivatives <00SC2863>. Aroyl-substituted ketene aminals 156 reacted with aryl azides to provide polysubstituted 1,23-triazoles 157 <00HC387>. 2-Aryl-2T/,4/f-imidazo[43-d][l,2,3]triazoles 159 were prepared from the reaction of triethyl AM-ethyl-2-methyl-4-nitro-l//-imidazol-5-yl phosphoramidate (158) with aryl isocyanates <00TL9889>. 

Anodic oxidation of the carbamates 17 and 23 in methanol, followed by reaction with chlorodiphenylphosphine affords the a-diphenylphosphinylcarbamates 20 and 25, from which the readily generated carbanions react with aldehydes to give the 4-phosphinyl-2-oxazolidinones 21 and 26. The removal of the diphenylphosphinyl group by a mild thermal treatment provides a route to the 2(3//)-oxazolones 22 and 27 (Fig. 5.6). ... 

Lead tetraacetate oxidative cyclization of the A-(l-naphthylvinyl)urethane 30, derived from I -acetonaphthone 28, yields 4-naphthyl-2(3//)-oxazolone 32 as the... 

Anodic oxidation of 2-oxazolidinones 81 in methanol using Et4N" OTs as a supporting electrolyte yields the 4-methoxylated derivatives 82 that undergo a facile elimination of methanol to give 2(3//)-oxazolones such as 83 and 84. ... 

The PCC oxidation of 3-amino-4,5-diphenyl-2(3//)-oxazolone 96 affords mono-diazobenzyl 286 as the primary decomposition product obtained via loss of carbon monoxide from the postulated A -nitrenolactam 285. Oxidation of 96 with tert-BuOCl/NEt3 at 108 °C results in a deep green solution of 285, which reacts with dimethyl sulfoxide (DMSO) to give the sulfoximide 288 (Fig. 5.68). ... 

Mechanistically, the authors proposed initial hydroxylation at C-5 followed by anion formation of the 5-hydroxyl group, attack at C-2 and rearrangement to the 2-amino-4(5//)-oxazolone upon work-up (Scheme 6.31). To support this premise they oxidized 112d to 118, which rearranged to 113d upon exposure to 5% aqueous ammonia at room temperature, consistent with previous work. ... 

TABLE 6.6. 2-AMINO-5-(CARBOXYALKYL)-4(5ff)-OXAZOLONES FROM OXIDATIVE RING CONTRACTION OE 2-AMINOPYRIMIDINONES ... 

Two different methods have also been described for the synthesis of 4-alkoxy-5(2//)-oxazolones 50. In the first case, 4-(phenylthio)-5(277)-oxazolones 48 are oxidized to the 4-phenylsulfinyl derivatives that react with the alcohol present in the reaction medium to afford the corresponding 4-alkoxy derivatives. Alternatively, 4-alkoxy-5(2//)-oxazolones 50 have been obtained by condensation of iminooxalates and ketones in acidic medium. (Scheme 7.12 Table 7.7, Fig. 7.8 Table 7.8, Fig. 7.9). 

Oxazolone At-oxides 91 have been obtained by heating a solution of 5-isonitroso-2,2-dimethyl-l,3-dioxane-4,6-dione 90 with the corresponding ketone in toluene. It has been postulated that the reaction occurs through an intermediate nitrosoketene that is generated from 90 via loss of CO2 and acetone, respectively. 

A new and completely different methodology involving a cycloaddition reaction has been described. The reaction between diphenylketene, ferf-butylcyanoketene or dimethylketene with 2,4,6-trimethylbenzonitrile A-oxide gave the corresponding 5(4//)-oxazolones 107 in moderate yields (Scheme 7.30). 

Michael Reaction. 5(47/)-Oxazolones undergo base-catalyzed conjugate addition to activated unsaturated compounds to afford the corresponding C-4 Michael adducts. For example, base-catalyzed addition of a 4-monosubstituted-5(4//)-oxazolone 157 to methyl propiolate yields a mixture of diastereomeric methyl 3-(5-oxo-2-phenyl-2-oxazolin-4-yl)acrylates 158. Hydrolytic ring opening of 158 and subsequent oxidation with lead tetraacetate affords 3-acylacrylates 160... 

Azine A1-Oxides. Quinoline and isoquinoline 7/-oxides react readily with 2-phenyl-5(47/)-oxazolone 209 (Rj = Ph) and 2-methyl-5(47/)-oxazolone 209 (Ri = Me) in the presence of acetic anhydride to afford 2-substituted 4-(quinol-2-yl)- 210 and 4-(isoquinol-l-yl)-5(4//)-oxazolones 211, respectively, in good yields... 

The oxidation by molecular oxygen or the base-catalyzed oxidative decarboxylation of saturated 5(4//)-oxazolones 278 yields diacylamines and provides an efficient procedure to prepare imides 279 from Al-acylamino acids (Scheme 7.90). 

Reaction of a-hydrazinoheterocycles with 4-(hydroxymethylene)-2-phenyl-5(4//)-oxazolone 406 gives rise to A-benzoyl-ot-(heteroaryl)glycinates 563 containing a fused 1,2,4-triazole after oxidative cyclization (Scheme 7.178). ... 

The reaction of nitrile oxides with 4-arylmethylene-5(4//)-oxazolones 675 to give the corresponding spiroisoxazoline oxazolones 676 is also well known.The regiochemistry of this cycloaddition reaction was initially incorrectly assigned but a careful study of the reaction showed that the regiochemistry of the 1,3-dipolar cycloaddition of nitrile oxides is the same as that observed with nitrile imines (Scheme 7.213). Examples of spiroisoxazoline oxazolones are shown in Table 7.49 (Fig. 7.60). 

TABLE 7.49. OXAZOLONE SPIROISOXAZOLINES FROM 1,3-DIPOLAR CYCLOADDITION REACTION OF UNSATURATED 5(4H)-OXAZOLONES WITH NITRILE OXIDES... 

If 4-(ethoxymethylene)-2-phenyl-5(47/)-oxazolone 403 is used as the dipolar-ophile, reaction with nitrile oxides yields cycloadducts 682 with reversed regio-chemistry. Further reaction of 682 can then yield 4-aminoisoxazoline-4-carboxylic acids 683 or 4-amino-3-arylisoxazoles 684 depending on the reaction conditions... 

The Diels-Alder reaction of (Z)-4-arylidene-2-phenyl-5(4//)-oxazolone 707 and Danishefsky s diene is best conducted in toluene at reflux to produce both the endo and the exo stereoisomers of 708. Base treatment of the cycloadduct mixture promotes aromatization through spontaneous oxidative decarboxylation to give 3-aryl-4-benzamidophenols that are converted to 3-aryl-4-aminophenols 709 by acid... 

Dipolar cycloaddition of 4-arylmethyleneisoxazol-5-ones 794 and 2-methyl-4-phenyl-5(4//)-oxazolone 795 leads to pyrrole-3-carboxyhc acids that have been isolated as hydroxamates 796. The authors carried out this cycloaddition-nitrile oxide addition as a one-pot reaction (Scheme 7.243). ... 

Condensation of A -acylglycines with carbonyl compounds, the Erlenmeyer synthesis, continues to be exploited to prepare of a wide variety of unsaturated-5(47/)-oxazolones. The reaction is performed in the presence of a cyclodehydrating agent and recently bismuth(lll) acetate has been evaluated in this capacity. Alternatively, unsaturated 5(47/)-oxazolones can be obtained from hippuric acid and a carbonyl compound or from the appropriate dehydroamino acid derivative using 3-(aIkoxycarbonyl)benzotriazole-l-oxides as the cyclodehydrating agent. 

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