Amino condensation with diketones

Amino-l-(p-toluenesulfonyl)pyrazole condenses with -diketones to yield acylaminocrotonate derivatives. These cyclize to pyrazolo[l,5-a]pyrimidines... 

Diamino-4//-1,2,6-thiadiazine 1,1 -dioxide (185) undergoes base-catalysed condensations with -diketones to yield 4-aminopyrido[2,3-c][l,2,6]thiadiazine 2,2-dioxides (186) <86CS607>, and Con-rad-Limpach type cyclization with -keto esters to yield 4-amino-l/7-pyrido[2,3-c][l,2,6]thiadiazin-5(8/f) Oite 2,2-dioxides (187) (Scheme 19) <88AQ89>. 

Many pyrazine and quinoxaline syntheses yield mono- or di-N-oxides (76H(4)769). The condensation of a-aminooximes with 1,2-diketones results in the direct formation of pyrazine mono-N-oxides. The a-aminooximes themselves are not easily prepared but 2-amino-2-deoxy sugars readily form the oximes, which have been condensed with glyoxal to yield the pyrazine 4-oxides (Scheme 18) (72JOC2635, 80JOC1693). 

Probably the most important reactant in the formation of volatile meat flavor compounds is hydrogen sulfide. It can be formed by several pathways during meat cookery, but one mechanism is Strecker degradation of cysteine in the presence of a diketone as established by Kobayashi and Fujimaki (29). The cysteine condenses with the diketone and the product in turn decarboxylates to amino carbonyl compounds that can be degraded to hydrogen sulfide, ammonia and acetaldehyde. These become very reactive volatiles for the formation of many flavor compounds in meat and other foods. 

A one-pot synthesis of pyrroles (90) from 1,2,5-selenadiazoles (88) with 1,3-diketones in the presence of zinc powder and acetic acid was reported. Initial reductive elimination of selenium gave a diamine (89), then one amino group was condensed with a 1,3-diketone followed by intramolecular cyclization to afford a pyrrole (90). [94JCS(P1)2201]... 

The condensation of amino acids esters with diketones leads to cylic derivatives. Limited success was achieved in this respect with acetyl acetone [262] amino acids were condensed prior to GC analysis with 2,5-hexanedione by Walle [263] (Scheme 5.24). The free carboxyl group of the reaction product was esterified with methanolic HC1. However, the procedure was applied to only a few amino acids. 

N-Heterocyclic jS-enamino esters which are unsubstituted in the 1-position are well suited for a double condensation reaction when treated with 1,3-dicarbonyl compounds to give annelation of a [1,2-a] pyrimidine ring. Thus, the condensation of 2-aminopyrroline affords pyrrolo[l,2-a]-pyrimidines.82,114 Shvedov et al. treated 2-amino-3-pyrrolecarbonitrile 187 with / -diketones or ethyl acetoacetate74115 to give 188. No ring closure... 

It has been reported that / -amino- and / -chloro-a/ -unsaturated ketones undergo condensation with sulfamide to yield 2//-l,2,6-thiadiazine 1,1-dioxides in superior yields to those obtained using ) -diketones <91S355>. With unsymmetrically substituted sulfamides enhanced yields and regio-selectivity are noted, particularly with the ) -chloro compounds (see Scheme 32). 

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