Ester enolates generation

Ester enolates generated by proton abstraction with dialkylamide bases add to aldehydes and ketones to give (3 hydroxy esters... 

Diastereoselectivity in the aldol and the conjugate additions of 2 -hydroxy-1,T-binaphthyl ester enolates with a variety of carbonyl electrophiles has also been explored the tendency of the ester enolates, generated by BuLi, to react with aldehydes to give threo products preferentially with high diastereoselectivity has been interpreted in terms of an acyclic transition state of chelated lithium enolate involving the aldehyde carbonyl and the 2 -hydroxy group. 

Conjugate addition reactions to the E-alkenoate proceeded fruitfully [293]. Remarkably, ketone enolates added to the alkenoate (Eq. 106) to afford the Michael adducts in the absence of the three fluorine atoms, the retro-Michael reaction dominates, because a ketone enolate is more stable that the ester enolate generated by the conjugate addition process therefore some special driving... 

HI hi acetic acid allows the reduction of jS-peracetates of the higher sugar N-acetylneuraminic acid to the corresponding anomeric deoxy compounds.277 At room temperature this method gave exclusively the a-anomer, whereas at —20 °C a 4 1 a [i ratio resulted. This may be explained by thermodynamic and kinetic protonation of ester enolates generated in situ from anomeric iodide in a manner reminiscent of previous reductions of 2-iodo sugar lactones.278... 

In the absence of monomer, GTP catalysts are destroyed by the initiator. A one to one molar mixture of bifluoride and MTS, for example produces methyl isobuterate, trimethylsilylfluoride, trimethylsilylmethoxide, methyl 2,2,4-trimethyl-3-oxopentanoate, and other oligomers [19, 26]. Seebach has shown that ester enolates generate ketenes at room temperature [27] (Scheme 16). These reactions support the dissociative mechanism wherein... 

Ester enolates generated by treatment of the corresponding esters with 1 equiv. of LiHMDS at -78 °C, were aminated by the chiral dialkylazodicarboxylates 97 at -78 °C (Scheme 46). 

If the cleavage of siloxycyclopropanes with fluoride anions could be performed under strictly anhydrous conditions, the ester enolate generated by ring opening should be interceptable by electrophiles different from protons. This process could be realized... 

An intramolecular tandem Michael aldol reaction was described for esters that have an enolizable aldehyde in the molecule. The lithium ester enolate generated through the Michael reaction undergoes an intramolecular aldol reaction. Thus, the reaction of unsaturated esters 153 with lithium benzylthiolate provided the expected cyclization products 156 and 157 via (w-formylenolate 154 in an excellent cis stereoselectivity (Scheme 49)no. 

Treatment of 88 with /-BuOK afforded the corresponding palladacycles 89 in good overall yield, as a mixture of two diastereosiomers (Equation 13). The stereoselective event involved an intramolecular displacement of the iodide by a potassium ester enolate generated in situ <20030M2961>. 

In the first step the base (usually an alkoxide, LDA, or NaH) deprotonates the a-proton of the ester to generate an ester enolate that will serve as the nucleophile in the reaction. Next, the enolate attacks the carbonyl group of the other ester (or acyl halide or anhydride) to form a tetrahedral intermediate, which breaks down in the third step by ejecting a leaving group (alkoxide or halide). Since it is adjacent to two carbonyls, the a-proton in the product p-keto ester is more acidic than in the precursor ester. Linder the basic reaction conditions this proton is removed to give rise to a resonance stabilized anion, which is much less reactive than the ester enolate generated in the first step. Therefore, the p-keto ester product does not react further. 

It is possible to construct tertiary alcohols in a one-step process from an a-1,2,4-triazol-1-yl ketone with a suitable carbanion (Figure 22). In this case the ester enolate generated using lithium diisopropylamide gives a much better yield than the product of the Reformatsky reaction. 

The following example involves the interaction between dithiocarboxylate sulfur and cyclopropane ring. Thus, treatment of the ester enolate, generated from (29), with carbon disulfide and... 

Pd complexes catalyze the arylation of ester enolates generated in situ in the presence of a base (Buchwald, Hartwig, Scheme 19.30b) [35]. Arylation of malonates proceeds under similar... 

Ester Enolates. Enantiomerically pure amino acids may ultimately be prepared via stereospecific ester enolate generation using an oxazolidine chiral auxiliary (eq 2). Moderate diastere-oselectivity is observed using potassium hexamethyldisilazide. 

Nishimura K, Ono M, Nagaoka Y, Tomioka K. Catalytic enantioselective protonation of lithium ester enolates generated by conjugate addition of arylthiolate to enolates. Angew. Chem. Int. Ed. 2001 40 440-442. 

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