Dicarbonyls, Group

This preparation describes a convenient and general method of synthesis of substituted pyrimidines from compounds containing a /3-dicarbonyl group, either intact or as the corresponding ketal. The usefulness of the 2-mercaptopyrimidines is enhanced by the ease of removal of the mercapto group by desulfurization 9 or oxidation 10 and its replacement by other functional groups.1 ... 

Table 1. Dications formed upon protonation of 1,3-dicarbonyl groups and related precursors.

Colorant formation may, therefore, be regarded as a polymerization process, which, as it proceeds, results in a shift of the absorption to the long wave lengths (red) and in a reduction in the intensity of the absorption. Such shifts are satisfactorily explained by structures, based on the conjugated a-dicarbonyl groups, in which the general conjugation is in-... 

Cyclopentene-l,4-dione is a very reactive dienophile in the Diels-Alder reaction and thus provides access to a variety of compounds containing the reactive /3-dicarbonyl grouping in a five-... 

Each step in the Robinson annelation is controlled by the various devices you have already met. In the conjugate addition step, the a,P-unsaturated carbonyl compound is usually butenone or another ketone and they are suitable Michael acceptors. There is much more variation in the enol equivalent. Compounds with 1,3-dicarbonyl groups are popular so ester groups can be added to ketones and removed afterwards by hydrolysis and decarboxylation. Keto-esters react well in the Robinson annelation. The ester group stabilizes the enolate but is not very electrophilic. In this example MeOK is the base for the conjugate addition and a weaker base is used for the aldol. 

Use this detector primarily for halogen-containing compounds. It also can be used for compounds containing an electron- deficient center, such as a nitro group, an alpha dicarbonyl group, S, or P, but with reduced sensitivity. 

In sharp contreist, however. Scheme 5 gives an instance of a methyl carbanion being introduced largely in an SN2 type inversion stereochemistry. Note that the substrate carries a cyclopropane carbon doubly activated by 1,3-dicarbonyl groups. A possible explanation is given in Scheme 6. The reaction can be utilized in the selective synthesis of dl-neonepetalactone and its epimer. 

Amino acid (31) is an intermediate in the synthesis of some 8-blockers. It contains 1,4-dicarbonyl groups and an amino group 1,3 to the ketone. If the amino group comes from a nitro group (32) then FGA (Chapter 24) gives a good disconnection to (33). 

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