2-Phenyl-4-ethoxymethylene oxazolone

A paste prepared from 4-ethoxymethylene-2-phenyl-5-oxazolone and tetrahydro-furan mixed with indoline 4-(5-indolinylmethylene)-2-phenyl-5-oxazolone. Y 80%. F. e. and steps s. H. Behringer and P. Duesberg, B. 96, 377 (1963). 

Ethoxymethylene)-2-phenyl-5(47/)-oxazolone 404, readily available from hippuric acid and triethyl orthoformate, has also been used as a starting material for other unsaturated oxazolones via addition-elimination reactions. Nitrogen nucleophiles are most commonly used and amines give rise to 4-(aminomethyl-ene)-2-phenyl-5(4//)-oxazolones 405 (Scheme 7.130 Table 7.37, Fig. 7.48) which, in many cases have been evaluated as antihypertensives. 

Reaction of 4-(ethoxymethylene)-2-phenyl-5(47f)-oxazolone 542 with a hydra-zide gives l-acyl-3-hydroxy-17/-pyrazoles 544 via an addition-elimination sequence to generate 543 followed by cyclization as shown in Scheme 7.171. ... 

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... 

R1 = R2 = H) gave the triazolo[l,5-a]pyrimidines (125), but with 124 (R1 = R2 = Me) afforded the dioxo derivative 126, and with a-cyano- y-butyrolactones (127) or 2-amino-3-ethoxycarbonyl-5,6-dihydro-4//-thiopyran (129) gave the triazolopyrimidines 128 and 130, respectively (81JHC1287). Treatment of 4-ethoxymethylene-2-phenyl-5(4//)-oxazolone (131) with 5-amino-3-methylthio-l//-1,2,4-triazoles gave the triazolo[l,5-a]pyrimidi-none 132 and the [4,3-a] isomer 133 (93H955) (Scheme 24). 

Tsuge and Noguchi469 prepared the 3-benzamido-4-oxo-4//-pyrido-[l,2-a]pyrimidine and its methyl substituted derivatives from 2-amino-pyridines and 2-phenyl-4-ethoxymethylene-5-oxazolone in boiling ethanol, without the isolation of the condensation products of type 94. The pyrido-pyrimidine was formed from 2-amino-6-methylpyridine, but in a longer reaction period and in low percentage yield. Condensation product 94 was cyclized in ethanol or polyphosphoric acid or acetic acid. 3-Benzamido-2-methyl-4-oxo-4A/-pyrido[l,2- ]pyrimidine was synthetized from 2-amino-pyridine and the appropriate oxazolone derivative. 

The exo double bond of 4-alkylidene and 4-arylidene-5(4//)-oxazolones undergoes cycloaddition reactions with 1,3-dipolar reagents. For example, nitrile oxides add to 2-phenyl-4-ethoxymethylene-5(4//)-oxazolone (88) to give spirocyclic products that may be hydrolyzed to 4-aminoisooxazoles... 

Ethoxymethylene-2-phenyl-5(4H)-oxazolone (26) has been shown to be a useful synthon for the synthesis of a range of fused-ring heterocycles by its reactions with suitable aminoheterocycles. Examples include the pyrazolopyrimidines (27) and (28) and others (Scheme 5) [93H(35)9S5]. 

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