Acetoacetates, enolization

The acetoacetate enolate ion (A in frame 54) is a reagent for the synthon B, the acetone anion. We shall discover how to add the COiEt activating group later. 

Figure 4.11 Molecular structures of typical crown-ether complexes with alkali metal cations (a) sodium-water-benzo-I5-crown-5 showing pentagonal-pyramidal coordination of Na by 6 oxygen atoms (b) 18-crown-6-potassium-ethyl acetoacetate enolate showing unsymmelrical coordination of K by 8 oxygen atoms and (c) the RbNCS ion pair coordinated by dibenzo-I8-crown-6 to give seven-fold coordination about Rb.

Hypothesis (A) is in contradiction with the experimental evidence, since glycolaldehyde andl, 3-dihydroxy-2-propanone (dihydroxyacetone)9 16 react in the same way as do the sugars. It is evident that these compounds do not possess two contiguous hydroxyl groups. Moreover, when methyl trans-0-(/3-D-glucopyranosyl)acetoacetate enol (LXIV) was treated with zinc chloride under the conditions used by West and by Garda Gonzalez, a... 

Medium Still basic. Sources The ethyl acetoacetate enolate anion has a p/ifabH of... 

Readily available methylthiomaleic anhydride reacts smoothly with dienes giving Diels-Alder adducts [e.g. (149) from 2-methyl-buta-1,3-diene] which are transformed to j8-keto-ester ketals, e.g. (150), by oxidative decarboxylation (cf. ref. 49). Intermediate (149) can also be converted into the corresponding a-methylene-ketone or oxidized to salicylic esters. a-Nitroacetoacetates (151) have been prepared by condensing a-nitroacetates with ketene diethyl acetal followed by hydrolysis of the acetoacetate enol ether thus formed. 

One possible retrosynthesis of a ketone is disconnection at the alpha carbon. The alpha carbon was the nucleophile (enolate), and the other carbon was the electrophile (an alkyl halide). If the TM is a derivative of acetone, then this disconnection leads to the enolate of acetone. Rather than using the unstable enolate of acetone in a synthesis, the use of the ethyl acetoacetate enolate as a synthetic equivalent is preferred. 

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