Carbonyl compounds carbanions from

Finally, the addition of the carbanion of 1-chloroalkyl p-tolyl sulfoxides 154 to carbonyl compounds gave the adducts 155, which were treated with alkyllithium such as f-C4H9Li to afford the one-carbon homologated carbonyls compounds 158, from their lithium enolate forms 157, having an alkyl group at the a-position, via the carbenoid /S-alkoxides 156 (equation 53) °. 

Olefin synthesis starts usually from carbonyl compounds and carbanions with relatively electropositive, redox-active substituents mostly containing phosphorus, sulfur, or silicon. The carbanions add to the carbonyl group and the oxy anion attacks the oxidizable atom Y in-tramolecularly. The oxide Y—O" is then eliminated and a new C—C bond is formed. Such reactions take place because the formation of a Y—0 bond is thermodynamically favored and because Y is able to expand its coordination sphere and to raise its oxidation number. 

Methyl group (Section 2 7) The group —CH3 Mevalonic acid (Section 26 10) An intermediate in the biosyn thesis of steroids from acetyl coenzyme A Micelle (Section 19 5) A sphencal aggregate of species such as carboxylate salts of fatty acids that contain a lipophilic end and a hydrophilic end Micelles containing 50-100 car boxylate salts of fatty acids are soaps Michael addition (Sections 18 13 and 21 9) The conjugate ad dition of a carbanion (usually an enolate) to an a 3 unsatu rated carbonyl compound... 

OC-All lation of Carbonyl Compounds and Derivatives. The organoborate iatermediates generated by the reaction of alkylboranes with carbanions derived from a-halocarbonyl compounds and a-halonitriles rearrange to give a-alkylated products. 

Carbanions derived from carbonyl compoimds are often referred to as etiolates. This name is derived from the enol tautomer of carbonyl compounds. The resonance-stabilized enolate anion is the conjugate base of both the keto and enol forms of carbonyl... 

Methylsulfinyl carbanion (dimsyl ion) is prepared from 0.10 mole of sodium hydride in 50 ml of dimethyl sulfoxide under a nitrogen atmosphere as described in Chapter 10, Section III. The solution is diluted by the addition of 50 ml of dry THF and a small amount (1-10 mg) of triphenylmethane is added to act as an indicator. (The red color produced by triphenylmethyl carbanion is discharged when the dimsylsodium is consumed.) Acetylene (purified as described in Chapter 14, Section I) is introduced into the system with stirring through a gas inlet tube until the formation of sodium acetylide is complete, as indicated by disappearance of the red color. The gas inlet tube is replaced by a dropping funnel and a solution of 0.10 mole of the substrate in 20 ml of dry THF is added with stirring at room temperature over a period of about 1 hour. In the case of ethynylation of carbonyl compounds (given below), the solution is then cautiously treated with 6 g (0.11 mole) of ammonium chloride. The reaction mixture is then diluted with 500 ml of water, and the aqueous solution is extracted three times with 150-ml portions of ether. The ether solution is dried (sodium sulfate), the ether is removed (rotary evaporator), and the residue is fractionally distilled under reduced pressure to yield the ethynyl alcohol. 

Other asymmetric syntheses, based on aldol condensation of chiral a-sulfinyl carbanions with carbonyl compounds, are the formation of / -hydroxyketones from /J-sulfinylhydrazones 166211-214, of /3, /l -dihydroxyketones from 3-(p-tolylsulfinyl-methyl)-A2-methylisoxalinones 167215, of /1-hydroxyacids from 2-(p-tolylsulfinylmethyl)oxazolines 168216 and of /J-hydroxyesters from ethyl-p-tolylsulfinyl-W-methoxyacetamide 169217. 

The procedure involves C-alkylation of an a-sulfonyl carbanion derived from 245 with alkyl halides or carbonyl compounds, followed by cleavage of the cyclopropanols 247 produced by deprotection of the hydroxy group of 246 to give (E)-substituted aldehydes141. 

The decarboxylation reaction usually proceeds from the dissociated form of a carboxyl group. As a result, the primary reaction intermediate is more or less a carbanion-like species. In one case, the carbanion is stabilized by the adjacent carbonyl group to form an enolate intermediate as seen in the case of decarboxylation of malonic acid and tropic acid derivatives. In the other case, the anion is stabilized by the aid of the thiazolium ring of TPP. This is the case of transketolases. The formation of carbanion equivalents is essentially important in the synthetic chemistry no matter what methods one takes, i.e., enzymatic or ordinary chemical. They undergo C—C bond-forming reactions with carbonyl compounds as well as a number of reactions with electrophiles, such as protonation, Michael-type addition, substitution with pyrophosphate and halides and so on. In this context,... 

Reaction of the carbanion of chloromethyl phenyl sulphoxide 409 with carbonyl compounds yields the corresponding 0-hydroxy adducts 410 in 68-79% yield. Each of these compounds appears to be a single isomer (equation 242). Treatment of adducts 410 with dilute potassium hydroxide in methanol at room temperature gives the epoxy sulphoxides 411 (equation 243). The ease of this intramolecular displacement of chloride ion contrasts with a great difficulty in displacing chloride ion from chloromethyl phenyl sulphoxide by external nucleophiles . When chloromethyl methyl sulphoxide 412 is reacted with unsymmetrical ketones in the presence of potassium tcrt-butoxide in tert-butanol oxiranes are directly formed as a mixture of diastereoisomers (equation 244). a-Sulphinyl epoxides 413 rearrange to a-sulphinyl aldehydes 414 or ketones, which can be transformed by elimination of sulphenic acid into a, 8-unsaturated aldehydes or ketones (equation 245). The lithium salts (410a) of a-chloro-/ -hydroxyalkyl... 

Other asymmetric syntheses, based on aldol condensation of chiral a-sulfinyl carbanions with carbonyl compounds, are the formation of -hydroxyketones from -sulfinylhydrazones of -dihydroxyketones from 3-(p-tolylsulfmyl-... 

Cyclopropyl sulfones were shown to be obtained either by cyclization of y-p-tosyloxy sulfones 232 with base or by treatment of phenylsulfonylacetonitrile 233a or ethyl phenyl sulfonyl acetate 233b with 1,2-dibromoethane in the presence of benzyltriethyl-ammonium chloride (BTEA) and alkali in good yields. Chang and Pinnick synthesized various cyclopropane derivatives 234 upon initial treatment of carbanions derived from cyclopropyl phenyl sulfone with either alkylating agents or a carbonyl compound and subsequent desulfonylation, as shown below. 

Carbanions derived from phosphine oxides also add to carbonyl compounds. The adducts are stable but undergo elimination to form alkene on heating with a base such as sodium hydride. This reaction is known as the Horner-Wittig reaction.268... 

Trialkylsilyl groups have a modest stabilizing effect on adjacent carbanions (see Part A, Section 3.4.2). Reaction of the carbanions with carbonyl compounds gives (3-hydroxyalkylsilanes. (3-Hydroxyalkylsilanes are converted to alkenes by either acid or base.270 These eliminations provide the basis for a synthesis of alkenes. The reaction is sometimes called the Peterson reaction.211 For example, the Grignard reagent derived from chloromethyltrimethylsilane adds to an aldehyde or ketone and the intermediate can be converted to a terminal alkene by acid or base.272... 

Amines, thiols, eOH (p. 226), etc., will also add to the 0-carbon atom of 0-unsaturated carbonyl compounds and esters, but the most important reactions of C=C—C=0 systems are in Michael reactions with carbanions reactions in which carbon-carbon bonds are formed. A good example is the synthesis of l,l-dimethylcyclohexan-3,5-dione (dimedone, 100) starting from 2-methylpent-2-ene-4-one (mesityl oxide, 101) and the carbanion 0CH(CO2Et)2 ... 

The initial carbon-carbon bond formation (— 84) is often reversible, and a subsequent step—such as dehydration—may be necessary to displace the equilibrium. The many different (often named) reactions really differ from each other only in the nature of the particular carbonyl compound (aldehyde, ketone, ester, etc.), and in the type of carbanion, employed. 

Here the carbanion (87), obtained from the action of base (usually eOH) on an oc-H atom of one molecule of a carbonyl compound (88), adds to the carbonyl carbon of another (88) to yield a -hydroxy-carbonyl compound. Thus with ethanal, CH3CHO, the product is 3-hydroxybutanal (89)—aldol itself ... 

An interesting intramolecular disnlacement occurs in the Darzens reaction, in which carbanions derived from a-haloesters react with carbonyl compounds to yield a-epoxyesters ... 

In a similar manner, starting from 2-methylchloride-naphtho[l,8-de][l,2,3]triazine and magnesium, via a novel sonication-promoted Barbier reaction, an a-aminomethyl carbanion equivalent is generated which reacts in situ with a variety of carbonyl compounds. Subsequent catalytic hydrogenolysis of the triazine moiety yields the corresponding amines <00TL4685>. Sterically controlled regiospecific cyclization of aldose-5-ethyl-l,2,4-... 

Trimethylsilylation of enolizable carbonyl compounds and alcohols has also been accomplished by the fluoride ion promoted reaction with hexamethyldisilane and ethyl trimethylsilylacetate [48, 49], with high stereospecificity giving Z-enol ethers from ketones [50]. l-Trimethylsilyl-(l-trimethylsilyloxy)alkanes, produced from the reaction of aldehydes with hexamethyldisilane, undergo acid-catalysed hydrolysis during work up to yield the trimethylsilylcarbinols [51]. In the case of aryl aldehydes, the initially formed trimethylsiloxy carbanion produces the pinacol (Scheme 3.1). 

Silylation using the silylacetate (3.1.14) [49] involves the initial formation of the acetate carbanion, which abstracts a proton from the carbonyl compound or alcohol (Scheme 3.2, Table 3.5). When the reaction with a ketone is conducted in the presence of an aldehyde, crossed aldol products are obtained (see Chapter 6). 

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