4-benzylidene-2-methyl-5 -oxazolone

Heterogeneous catalysts modified by the addition of chiral substances have been used to hydrogenate olefins asymmetrically, but only a few effective chiral heterogeneous catalyst systems have been found. Palladium deposited on silk fibroin was used to hydrogenate 4-benzylidene-2-methyl-5-oxazolone asymmetrically to give, after hydrolysis, optically active phenylalanine (Fig. lc). The optical purity1 of the product was found to be dependent on the origin of the fibroin and its chemical pretreatment (4-6). 

When 4-benzylidene-2-methyl-5-oxazolone (45) is prepared by the Erlenmeyer procedure, a light yellow product is generally isolated. Rufenacht showed that pure 45 is white and that the colored... 

Hippuric acid has often been replaced in these reactions by A-acetylglycine Herbst and Shemin,964 for example, used it with benzaldehyde when preparing 4-benzylidene-2-methyl-5-oxazolone in 75% yield. 

The reaction of 2-phenyl-4-benzylidene-5-oxazolone with hydrazine forms 4-benzamido-5-phenyl-3-pyrazolidinone.319,1342 Both 2-pyrazolin-5-ones and 3-pyrazolin-5-ones have been reduced catalytically to 3-pyrazolidinones.1491,1592 Heymons and Rohland647 have treated 3-methyl-l,2-diphenyl-3-pyrazolin-5-one with sodium and carbon dioxide and claimed to have obtained a carboxylic acid, presumably by intermediate addition of sodium to the double bond (eq. 246). A number of... 

On the other hand, addition of diazomethane to the ester 18 [from (Z)-4-benzylidene-2-methyl-oxazolone and ( —)-iV-methylephedrine] and photolysis of the resultant 4,5-dihydro-3/f-pyr-azole gave a 57% yield of a mixture of diastereomers (66 34). Separation of the major dia-stereomer 19 by column chromatography and hydrolysis gave (— )-l-amino-2-phenylcycloprop-ane-1-carboxylic acid (-)-(17). ... 

Oxazol-5(2H)-one, 2-benzylidene-4-methyl-tautomerism, 6, 186 Oxazol-5(2ff)-one, 2-methylene-isomerization, 6, 226 Oxazol-5(2H)-one, 2-trifluoromethyl-acylation, 6, 201 Oxazol-5(4ff)-one, 4-allyl-thermal rearrangements, 6, 199 Oxazol-5(4H)-one, 4(arylmethylene)-Friedel-Crafts reactions, 6, 205 geometrical isomerism, 6, 185 Oxazol-5(4ff)-one, 4-benzylidene-2-phenyl-configuration, 6, 185 photorearrangement, 6, 201 Oxazol-5(4ff)-one, 4-benzyl-2-methyl-Friedel-Crafts reactions, 6, 205 Oxazol-5(4ff)-one, 4-methylene-in amino acid synthesis, 6, 203 Oxazol-5(4ff) -one. 2-trifluoromethyl-hydrolysis, 6, 206 Oxazolones... 

The member of this class which has been studied most thoroughly is 2-benzylidene-4-methyl-5(2 )-oxazolone (57). This compound may be prepared by ring closure of either 3-bromo-2-phenylacetamido-propionic acid or A-(a-halophenylacetyl)alanine (56) [Eq. (30)]. These reactions presumably proceed via unstable halogeno-5(4IT)-oxazolones, which rapidly lose hydrogen halide. 

Deacetylation of 4-[(o-acetoxy)benzylidene]-2-phenyl-5(47/)-oxazolone also immediately affords 602. The starting oxazolone was obtained by cyclodehydration of the corresponding cinnamic acid precursor or by condensation of hippuric acid with 2-acetoxybenzaldehyde in the absence of base. In examples using 2-hydroxy-acetophenone, 4-methyl-3-(acylamino)coumarins are obtained. ... 

It is well known that hydrogenation of dehydroamino acid derivatives derived from ring opening of unsaturated 5(4H)-oxazolones affords new racemic amino acids and, in some cases, enantiomerically pure compounds. On the other hand, a number of attempts have been made to hydrogenate the double bond of the unsaturated oxazolone itself. For example, 4-benzyl-2-methyl-5(4//)-oxazolone was prepared from 4-benzylidene-2-methyl-5(4H)-oxazolone using Raney Ni as a catalyst. This process is reported to be a general procedure to prepare saturated oxazolones directly (Scheme 7.194). 

Although it is well known that sulfur nucleophiles are excellent candidates for Michael reactions, they have scarcely been examined with unsaturated oxazolones. Nevertheless, 4-methyltoluene-a-thiol reacts with 4-benzylidene-2-methyl-5 (4//)-oxazolone 614 to give 615 as a mixture of erythro and threo isomers (Scheme 7.197). ° ... 

Electrochemical reduction of 4-benzylidene-2-methyl-5(47/)-oxazolone to produce racemic Al-acetylphenylalanine has been accomplished using lead and cadmium cathodes. ... 

The phenyl group of trisubstituted 4-benzylidene-5(4//)-oxazolones is nearly planar whereas the styryl moieties in (Z)-2-phenyl-4-(a-phenylethylidene)-5(4//)-oxazolone and fZ)-2-methyl-4-(a-phenylethylidene)-5(4//)-oxazolone show significant deviations from planarity. ... 

In the context of the nucleophihc ring-opening reactions, the mechanism of the reaction of 4-benzylidene-2-methyl-5(4/l/)-oxazolone with n-butylamine has been studied. 

H)-OxazoIones (78) are unstable with respect to the 4//-isomers (79) however, the 2-trifluoromethyl derivatives are unique in that the 2//-forms (78 R1 = CF3) are favoured (62LA(658)128). This was evident from the NMR spectra of numerous derivatives containing phenyl or alkyl groups at C(4) (64CB2023). While 2,2-disubstituted 5(2//)-oxazolones (80) have a fixed structure, the 2-methylene derivatives, such as 2-benzylidene-4-methyl-5(2H)-oxazolone (81), are in potential tautomeric equilibrium with 5(4//)-oxazolones, e.g. (82). However, compound (81) exists entirely in this form, no doubt because it is stabilized by conjugation of the phenyl group with the exocyclic double bond. 

Hydrazino-5,6-diphenyl-l,2,4-triazine (289) reacts with 4-benzylidene-2-phenyl-5(4//)-oxazo-lones (290) and 4-benzylidene-3-methyl-5(4//)-isoxazolones (291) in toluene to products (292), (293) substituted in the hydrazino group, the first by acylation by the oxazolone, the second by arylraethylidene group transfer (Scheme 53) <88JHC1813>. 

Benzyl.4.benzyliden.oxazolon-(S) 27, 226. 2-PhenyI.4-[4-methyl-benzyUden]-oxazo lon.(5) 27 I 299. 

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