Oxazoles palladium® acetate

Oxazoles can be arylated at either C-2 or C-5, the method shown being notable for the use of water as solvent. 2-Substitution of 5-aryl oxazoles, using palladium acetate, can be carried out without an added ligand. ... 

Whereas diazoacetic ester reacts with acrylonitriles at room temperature to give 2-pyrazolines (136), above 100 °C the cyclopropanes (138) are formed quantitatively, the 1-pyrazoline (137) being an intermediate. When the reaction is catalysed by palladium acetate, the oxazoles (139) are formed. ... 

Arylation of Thiazoles and Oxazoles. The protocol that was previously developed for the C-H activation of azine and diazine (V-oxides with aryl triflates was used to effect the arylation of flve-membered ring heterocycles, such as oxazoles and thiazoles. In contrast to another protocol that was previously reported by the same group, the transformation did not require an V-oxide function. However, in order to direct the arylation at the C4-position, to prevent the formation of a mixture of regioisomers, and to minimize the generation of diarylated products, a C5-chloride was used as a blocking group. The procedure, which is promoted by palladium acetate and di-tert-butyl(methyl)phosphonium tetrafluoroborate, uses an aryl bromide as the electrophile. 

Direct Alkenylation. A C2-alkenylation of purines and heteroarenes including oxazole utilizing styryl bromide was reported. Palladium acetate and Cul function as co-catalysts ... 

Palladium-catalyzed Direct Arykaion ofThiazoles, Benzoth-iazoles, Oxazoles, Benzoxazoles, and Imidazoles. Using palladium acetate as a catalyst and a phosphine as a ligand, thia-zole was diarylated at positions 2 and 5 (eq 16). A survey of... 

A unique Pd(II)-promoted ortfto-esterification of 2,5-diphenyloxazole has been described [26], When 2,5-diphenyloxazole was heated with 2.5 equivalents of Pd(OAc>2 in acetic acid and CCLt, regioselective palladation took place, giving rise to arylpalladium(n) o-complex 31 in almost quantitative yield. The regioselectivity observed reflects the strong coordination ability of the oxazole nitrogen atom to the palladium atom. Complex 31 was then dissolved in MeOH-THF (1 1) and the solution was stirred at 0 °C to produce 2-(5 -phenylthiazol2-yl)-benzoate 32. A... 

In contrast, if the mixture of 892 893 was transmetalated at —78°C with ZnCli and the resulting organozinc species quenched with D4-acetic acid, > 85% of the deuterium incorporation was found at C(2). The authors concluded that this organozinc species was best represented as the oxazole 895, which was subsequently used in palladium-catalyzed cross-coupling reactions (see Section 1.4.8). 

Last but not least, formation of the oxazole 35 has been observed in the reaction of methacrylonilirile (34) and diazoacetate catalyzed by palladium(II) acetate (Scheme... 

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