Pyrazine acylation

Dimethyl-188 and 2,6-dimethylpyrazine react very similarly to methylpyrazine. Thus, 2,6-dimethylpyrazine can be converted into a monoanion with sodamide in liquid ammonia which can be condensed with aldehydes and ketones,179 acylated with esters,181 and alkylated with alkyl halides181 to give the corresponding 2-methyl-6-substituted pyrazines. Acylation under suitable conditions also yields diacylated derivatives. Thus, when 2,6-dimethylpyrazine, sodamide, and ethyl benzoate are reacted in 1 3 2 molecular proportion, 38% 2,6-diphen-acylpyrazine (35) and 25% 2-methyl-6-phenacylpyrazine (36) is obtained. From the preparative point of view it is better to form the diacyl derivative by the further acylation of the monoacyl derivative rather than by direct diacylation.187... 

Both 2- and 3-methyl groups in pyrido[2,3-Z ]pyrazines are acylated by ethyl oxalate (71TH21500). They give (preferentially 3-) styryl derivatives with aromatic aldehydes and oximes with pentyl nitrite. 

Pyrido[2,3-6]pyrazine, 8-hydroxy-tautomerism, 3, 250 Pyrido[2,3-h]pyrazine, methyl-acylation, 3, 253 Pyrido[2,3-6]pyrazine, 2-oxo-oxidation, 3, 250-251... 

Acetyl-3-(perhydropyrido[l, 2-u]pyrazin-2-yl)-1 //-indole was deacety-lated in boiling MeOH in the presence of NaOH, and the product, 3-(perhydropyrido[l,2-u]pyrazin-2-yl)-l//-indole was N-acylated with different arylsulfonyl chloride in THF at 0°C in the presence of (Me3Si)2NNa (99MIP12, 01USP6251893)). 

Acylation of 3-arylamino-4-arylimino-4//-pyrido[l,2-u]pyrazines (373) with acyl chlorides afforded mixtures of mono- and bisacylated derivatives 374 and 375 (99JPR332). Acetyl chloride gave only monoacylated product 374 (R = 4-MePh, R =Me). Bis-acylated derivative 375 (R = 4-MePh, r = Me) was obtained in 68% yield in boiling toluene. Reaction of 373 with dienophiles 376 and 377 gave 4-thiono and 4-seleno derivatives of 4//-pyrido[l,2-u]pyrazines 378 (Y==S, Se) and 4-imino-4//-pyrido[l,2-u]pyrazines 379, respectively (99JPR332). 

Amine bound to a Wang-polystyrene resin 381 was acylated with 4-oxo-4Ff-pyrido[l,2-u]pyrazine-3-carboxylic acid in the presence of bromotrispyrrolidinophosphonium hexafluorophosphate and /-Pr2NEt in A-methylpyrrolidone (98MIP16). l-(4-Cyclohexyl-4-r / r-butylaminocarbo-nyl-l-piperidyl)-2-(4-fluorophenyl)ethylamine was acylated with perhydro-pyrido[l,2-u]pyrazine-3-carboxylic acid (01MIP19). An amino group of a macrocyclic compound attached to a solid support was acylated with... 

Methyl pyrazine-2-carboxylic acid is refluxed with thionyl chloride in anhydrous benzene for approximately 12 hours. Benzene and thionyl chloride excess is removed by distillation. Then some anhydrous dioxane is added and this acid chloride solution is allowed to drop into p-(/3-aminoethyl)-benzenesulfonamide suspension in dioxane and anhydrous pyridine. The resulting mixture is then refluxed for 3 hours. Dioxane is removed by distillation and then the residue is washed with water and acetic acid. The raw acylated sulfonamide is then filtered and crystallized from 95% ethanol, thus obtaining a product of MP 200 to 203 C. 

Oxazoles (191) are producedwhen triphenylphosphine is treated simultaneously with an a-azidocarbonyl compound and an acyl halide. The intermediate iminophosphoranes (189) react with the acyl halide before they can react with themselves to give pyrazines. Elimination of phosphine oxide from the resulting salts may give the intermediate halo-genoimines (190), or the oxazoles may be formed via the betaines (192). 

Acylation of the piperazine nitrogen atoms of 47/,87/-bis[l,2,5]oxadiazolo[3,4- 4 -< ]pyrazine 59 with acetyl bromide proceeds smoothly in the presence of pyridine in acetonitrile to give 60 (Equation 9) <1997CHE618>. 

A new synthesis of pterins based on the acylation of 4-amino-5-nitrosopyrimidines with dienoic acid chlorides, followed by a high-yielding intramolecular hetero DA cycloaddition and cleavage of the N—O bond has been reported <06HCA1140>. Several new substituted pterins have been obtained in an efficient one-pot procedure using N,N dimethyldichloromethyleniminium chloride (phosgeniminium chloride) and a suitable pyrazine <06H933>. 

In contrast to the previous transformations where the reaction took place at the five-membered ring, acylation of 182 at the pyrazine nitrogen atom was reported <1995FA405> to yield 183. 

Alkylpyrazines are prepared by two main procedures, (1) self-condensation of a-amino carbonyl compounds and (2) alkylation (or acylation) of pyrazines at nuclear or side chain carbons. Condensation of aminoacetone hydrochloride (491) in the presence of the corresponding aldehyde gave the 3- -alkyl-2,5-dimethylpyrazines 20e and 20g (Scheme 61) 36). 2,5-Dimethylpyrazine 20a was prepared from hydroxyiminoacetone (493) by reduction with tin and hydrochloric acid (Scheme 61) 145). 3-Ethyl-2,6-dimethylpyrazine (21b) was prepared along with 20a and 495 by condensation of aminoacetone hydrochloride (491) with 2-aminopentan-3-one hydrochloride (494) in the presence of sodium ethoxide (Scheme 61) 36). 

---