Reduction enolates generation

Reformatsky-type reactions and reductions. Enolates generated from a-bromoketones by reaction with BiClj-Al in an aqueous medium condense with various aldehydes to give J-hydroxy ketones." A modification of reaction conditions (BiClj-NaBH ) and in the absence of aldehydes leads to hydrodehalogenation of the haloketones. ... 

As noted in Chapter 1, this is one of the best methods for generating a specific enolate of a ketone. The enolate generated by conjugate reduction can undergo the characteristic alkylation and addition reactions that are discussed in Chapters 1 and 2. When this is the objective of the reduction, it is important to use only one equivalent of the proton donor. Ammonia, being a weaker acid than an aliphatic ketone, does... 

Lithium-ammonia reduction of a,/ -unsaturated ketones (entry 6, Scheme 1.4) provides a very useful method for generating specific enolates.26 The desired starting materials are often readily available, and the position of the double bond in the enone determines the structure of the resulting enolate. This and other reductive methods for generating enolates from enones will be discussed more frilly in Chapter 5. Another very important method for specific enolate generation, the addition of organometallic reagents to enones, will be discussed in Chapter 8. 

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... 

Reductive acylation of enones.1 The lithium enolate generated by reduction of enones with Li/NH, is converted to a (1-keto ester by reaction with this reagent in ether (THF promotes O-acylation). 

Procter reported the diastereoselective spirocyclisation of unsaturated ketones 163 using Sml2-43 165 The cyclisation proceeds by conjugate reduction, Sm(III) enolate generation and chelation-controlled aldol cyclisation to give, vyrt-spirocyclic cyclopentanols 164 in good yield (Scheme 5.106). It is important... 

The enolate, generated by TBAF cleavage of the enoxysilane derived from phenylselanylacetone, was trapped with benzaldehyde [39] (Scheme 33). The antUsyn ratio of diastereoisomers, easily identified by and Se NMR, was dependent on the temperature and the E or Z structure of the substrate. The borane reduction followed by a conventional acetonization led to a protected syn, syn-l,3-diol. 

Lithium or copper enolates, generated in situ by conjugate reduction of afi-unsaturated ketones, may be trapped by MeSSMe, PhSSPh, or PhSCl to give the /S-ketosulphide. /3-Keto-sulphides and -selenides are available on chloral-alumina oxidation of the corresponding /3-hydroxy compounds. The latter compounds may be prepared by alumina-promoted epoxide ring opening by thiols and selenols (Scheme 16). ... 

Some examples of regioselective alkylations of simple ketones are presented in Scheme 1.6. These examples illustrate the most useful modes of enolate generation, including deprotonation (entries 3 and 4), enone reduction (entries 1, 2, and 5), and cleavage of silyl enol ethers (entries 6 and 7). 

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