Reaction of a,3-Dicarbonyl Compounds with Ammonia

A series of 3-hydroxy-2,5-bis(p-alkylphenyl and p-alkoxyphenyl)pyrazines has been prepared, each in small yield, from p-substituted phenylglyoxals and ammonia (283) benzil and liquid ammonia (and ammonium chloride or potassium amide) have been shown to give low yields of tetraphenylpyrazine (284) and benzoyl-formoin, which has been claimed to have an enediol [PhCOC(OH)=C(OH)COPh] content of 90%, and ammonia gave 24rydroxy-3,5-diphenylpyrazine (285). 

Bisulphite Compounds of a-Hydroxy imino Ketones with Potassium Cyanide 

Gastaldi (286) first described this synthesis, in which an a-hydroxyimino ketone was treated with aqueous sodium bisulfite saturated with sulfur dioxide, and the bisulfite compound treated with potassium cyanide followed by hydrolysis with hydrochloric acid. By this procedure, Gastaldi prepared 2,5-dicyano-3,6-dimethyl-pyrazine from hydroxyiminoacetone, and 2,5-dicyano-3,6-diphenylpyrazine and some 3-cyano-2,5-diphenylpyrazine from hydroxyiminoacetophenone. He proposed a reaction mechanism involving the intermediate compounds (21) and (22). Sharp and Spring (287) used the same procedure to prepare 2,5-dicyano-3,6-diethyl-pyrazine from ethyl hydroxyiminomethyl ketone. 

The Gastaldi reaction has been investigated by Golombok and Spring (288), who pointed out that the self-condensation of a-amino ketones (proposed by Gastaldi) 

Hydrolysis of Acetamidoacetone Derivatives Formed from o-Amino Acids, Acetic Anhydride, and Pyridine 

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The preparations of hydroxypyrazines by primary syntheses have been described in Chapter II, and are summarized briefly, together with further data, as follows Section II.IG, from the reaction of a, 3-dicarbonyl compounds with ammonia [282 (cf. 281, 280), 283, 285] with additional information (1042, 1043) Section II.IM, from 1,2-dicarbonyl compounds with a-amino acids (311) Section II.IN, from a-amino acids through piperazine-2,5-diones (93,95,101,282,312,313)with additional data (843) Section 11.10, from aldehyde cyanohydrins ( ) [317-319 (cf. 282)1 and Section II.IP, from o-nitromandelonitrile and ethereal hydrogen cyanide (325). The preparations from a,iJ-dicarbonyl compounds with a,/ -diamino compounds are described in Section 11.2 (60, 80, 358, 359, 361-365b, 365d, 366-375) additional data have also been reported (824, 825, 827,845,846,971, 1044, 1045) and some reaction products have been isolated as the dihydro-pyrazines (340,341,357). 

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