A,y-diketo esters

If this type of condensation is carried out with hydrazinoisocytosines (182) and a,y-diketo esters, l//-pyrimido[4,5 -c ]-l, 2-diazepines (183) are formed as the major products. Only a small amount of pyrimido[4,5-c]pyridazines (184) can be isolated from these reactions (82JOC667). 

Reaction with a,y-diketo esters. The reaction of CNSifCHOi with the a, y-diketo ester 1 can be controlled to give one of the two possible adducts. 

If the acylating ester is diethyl oxalate, then an a,y-diketo ester, or a substituted glyoxalate, is formed. " These substances are important intermediates in the synthesis of certain /3-keto esters (method 307). 

Asymmetric hydrogenation. a-Hydroxy lactones and yacetamino-P-hydroxy esters in chiral form are created from a,y-diketo esters and 4-acetamino-3-keto-4-alkenoic esters, respectively, on hydrogenation. 

Carboxyalkyl-Y-but5U olactone has also been S5mthesized by combining pure enz5mies and whole microbial cells in the same process. Thus, the corresponding 2-hydroxy esters and lactones were obtained from 2-oxoglutaric acid [219]. Low ee values, however, were obtained for the reduction of a,y-diketo esters and keto a,y-diesters [220-224]. 

Note It is important to observe that the ester of a,y-diketo acid chemoselectively affords only y-oxime since the a-keto group is completely enolized (Scheme 7.7). It is also worth mentioning that inversion of the reactivity of two carbonyl groups is possible on lactonization. Within stable enol-lactone, the a-carbonyl group then reacts. 

The enzyme-catalyzed regio- and enantioselective reduction of a- and/or y-alkyl-substituted p,5-diketo ester derivatives would enable the simultaneous introduction of up to four stereogenic centers into the molecule by two consecutive reduction steps through dynamic kinetic resolution with a theoretical maximum yield of 100%. Although the dynamic kinetic resolution of a-substituted P-keto esters by chemical [14] or biocatalytic [15] reduction has proven broad applicability in stereoselective synthesis, the corresponding dynamic kinetic resolution of 2-substituted 1,3-diketones is rarely found in the literature [16]. 

By using active peptide esters with high molecular ester components, inter-molecular aminolysis can be suppressed. — E Glycyl glycine cross-linked poly-(4-hydroxy-3-nitrostyrene) ester hydrobromide suspended in dimethylformamide, neutralized with triethylamine, allowed to stand 12 hrs. at room temp., and the resulting poly-4-hydroxy-3-nitrostyrene removed by filtration diketo-piperazine. Y 75%. F. e. and ester components s. M. Fridkin, A. Patchornik, and E. Katchalski, Am. Soc. 87, 4646 (1965) peptides s. T. Wieland and G. Birr, Ang. Gh. 78, 303 (1966) with active a-aminocarboxylic acid polyphenolesters s. M. Fridkin, A. Patchornik, and E. Katchalski, Am. Soc, 88, 3164 (1966). 

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