Esters enoiates

C. Reactions of Magnesium Ester Enoiates and Magnesium Lactone Enoiates... 

Synthesis of p-Lactones by Aldolization of Ketones with Phenyl Ester Enoiates 3,3-Dimethy -1-oxaspiro(3.5]nonan-2-one. 

A new access to a-damascone by selective kinetic protonation of a-ketone enoiate, formed by reaction of an ester enoiate with nucieophiles, has recently been described by Fehr and Galindo [22] (scheme 2). 

B. Diastereoselective Additions of Ester Enoiates to Carbonyi Groups... 

Lithium ynoiates from iithium ester enoiates... 

Although metal ynoiates are equivalents of metallated ketenes, direct metallation of ketenes is often troublesome. Metallation of the precursors of ketenes, followed by transformation into the metallated ketenes, would be a better route to metal ynoiates. Based on this concept, an efficient method for the synthesis of lithium ynoiates has been developed, taking advantage of the properties of ester enoiates, which are easily converted into ketenes by elimination of alkoxides (equation 11) . The synthetic methods for lithium ynoiates via the cleavage of ester dianions are both convenient and quite general, because alkyl-, aryl- and sQyl-substimted lithium ynoiates can be synthesized in good yields. 

The a-bromo esters 39 are treated with LDA to form the bromo ester enoiates 40, which are subjected to lithium-halogen exchange with t-BuLi (3 equiv) at —78 °C. The resulting dilithium ester dianions 41 are thermally cleaved at 0 °C into the ynoiates 42 in good yields (equation 12). This procedure finally regenerates LDA from diisoprpylamine and t-BuLi along with the lithium ynolate (equation 12 ). 

An alkylation reaction is used to introduce a primary alkyl group onto i a position of a ketone, ester, or nitrile by 8 2 reaction of an enoiate ion with an alkyl halide. Thus, we need to look at the target molecule and identify any primary alkyl groups attached to an a carbon. In the present instance, the target has an a methyl group, which might be introduced by alkylation of an ester enoiate ion with iadomethane. 

RLi (R = 1 2°, 3° alkyl aryl vinylic alkynyl ester enoiate)... 

Summary This is an exampie of an Aidoi reaction, which resuits in the condensation of an aidehyde with an ester enoiated to give... 

P-keto ester enoiate (anion stabiiised by resonance)... 

II II The negative charge in the p-keto ester enoiate ion is stabilised by... 

FIGURE 19.99 In the first step of the reaction between an ester enoiate and an ester, the nucleophilic ester enoiate adds to the electrophilic carbonyl carbon of the ester. In the second step the alkoxide ion is lost from the tetrahedral intermediate. 

I Intramoiecuiar nucieophiiic addition of the ester enoiate ion to the carbonyi group of the second ester at the other end of the chain then gives a cyciic tetrahedrai intermediate. 

Syn-selective aldol reactions involving directly generated thiol ester enoiates were reported to give moderate to good selectivity and moderate yield, as shown in Table 2.11 [29]. Modest anti-selectivity was obtained in reactions of 2-pyridylthiopropionate (entry 7), suggesting the 2-pyridyl moiety could be coordinating with titanium. 

The reactions of a-thio-substituted ester enoiates have been reported to give moderate to excellent selectivity and moderate to good yield, as shown in Table 2.12 (entries 1-6) [29]. Interestingly, for a-substituted propionates (entries 4-6), selectivity was good to excellent for the product in which the... 

Kazmaier reported the synthesis of several racemic a-aminoaldols in which the a-amino group and the j5-hydroxyl group are anti [63]. Reactions of N-benzyloxycarbonyl amino acid ester enoiates with a variety of aldehydes afforded moderate to good yields and good to excellent diastereoselectivity as shown in Table 2.32. Titanium enoiates were generated by deprotonation of 179 with LDA in THF followed by the addition of 2 equiv. Ti(Oi-Pr)3Cl in THF at -78 °C. 

Figure 14.2 Propagating chain end of living poly(meth)acrylates and ester enoiate.

Reaction of zinc ester enoiates with conjugated enones... 

In addition to ester enoiates, ketone enoiates and nitronates also add to 3-thiazolines in the presence of BF3-Et20. Reactions of ketone enoiates have been cleverly exploited in the synthesis of 2,3,5-trisub-stituted thiophenes (260) by hydrolysis of adducts (259) and spontaneous cyclization to liberate water and ammonia (Scheme 52 Table 30). The 5-substituent of the thiophene is derived from the 5-substi-... 

Catalytic Enantioselective Mannich Reactions, Ester Enoiate-lmlne Condensations 3S9... 

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