Ketones, RCOR

When the doubly bonded oxygen is regarded as a substituent along the parent chain or ring, it is called an oxo group, =0, 

Exercise 7-7 Write appropriate structures corresponding to the following names. Show stereochemistry where specified. 

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Aldehydes and ketones RCOR react with oc-methoxyvinyllithium CH2= C(Li)OMe to give hydroxy enol ethers RR C(OH)C(OMe)=CH2, which are easily hydrolyzed to acyloins, RR C(OH)COMe. this reaction, the CH2=C(Li)OMe is a synthon for the unavailable H3C—C=0. The reagent also reacts with esters RCOOR to give RC(OH)(COMe=CH2)2- A synthon for the Ph—C=0 ion is PhC(CN)OSiMe3, which adds to aldehydes and ketones RCOR to give, after hydrolysis, the a-hydroxy ketones, RR C(OH)-COPh. °... 

Finally, note that the competition between 1C and ISC is believed to be a general feature in the photochemistry of ketones RCOR [73], of which CH2O is the simplest member. There is evidence that pathway branching to the So state is... 

A quite different and complimentary approach is to assume that addition of a nucleophile to an acyl derivative (RCOX) would follow the linear free energy relationship for addition of the nucleophile to the corresponding ketone (RCOR, or aldehyde if R=H) if conjugation between X and the carbonyl could be turned off, while leaving its polar effects unchanged. This can be done if one knows or can estimate the barrier to rotation about the CO-X bond, because the transition state for this rotation is expected to be in a conformation with X rotated by 90° relative to RCO. In this conformation X is no longer conjugated, so one can treat it as a pure polar substituent. Various values determined by this approach are included in the tables in this chapter. 

With aldehydes (and with unsymmetrical ketones, RCOR ) there is, of course, the possibility of forming alternative syn and anti geometrical isomers ... 

Figure 7-11 shows a Friedel-Crafts acylation reaction. The reaction produces an aryl ketone, which is useful in synthesis because it makes it relatively easy to convert the ketone (RCOR) group to an alkyl (R) group. The procedure involves the catalytic hydrogenation of the aryl ketone, and it s particularly useful when the electrophile in a Friedel-Crafts alkylation is susceptible to rearrangement. 

R can be aryl or saturated or unsaturated alkyl. Since the cyanohydrins1476 are easily formed from aldehydes (6-49) and the product is easily hydrolyzed to a ketone, this is a method for converting an aldehyde RCHO to a ketone RCOR 1477 (for other methods, see 0-97, 0-105, and 8-9).1478 In this procedure the normal mode of reaction of a carbonyl carbon is reversed. The C atom of an aldehyde molecule is normally electrophilic and is attacked by nucleophiles (Chapter 16), but by conversion to the protected cyanohydrin this carbon atom has been induced to perform as a nucleophile.1479 The German word umpolunglm is used to describe this kind of reversal (another example is found in 0-97). Since the ion 120 serves as a... 

Aldehydes and ketones RCOR react with a-methoxyvinyllithium CH2=C(Li)OMe to give hydroxy enol ethers RR C(OH)C(OMe)=CH2, which are easily hydrolyzed to acy-loins RR C(OH)COMe.597 In this reaction, the CH2=C(Li)OMe is a synthon for the un-... 

RC(OH)(COMe=CH2)2- A synthon for the Ph—0=0 ion is PhC(CN)OSiMe3, which adds to aldehydes and ketones RCOR to give, after hydrolysis, the a-hydroxy ketones RR C(OH)COPh.599... 

A closely related synthesis of /8-hydroxy esters is provided by the Refor-matsky reaction. This synthesis starts with an aldehyde or ketone, RCOR, and an a-bromo ester, such as ethyl bromoethanoate. Zinc in a nonhydroxylic solvent (usually benzene) transforms the bromo ester into an organozinc compound, which then adds to the aldehyde or ketone carbonyl. Hydrolysis produces the /3-hydroxy ester ... 

Table 1. Enantioselectivities for the hydrogenation of simple ketones RCOR .

Baeyer-Villiger oxidation Ketones (RCOR ) are oxidized by peracids (or peroxy acids, RCO2OH) to give esters (RC02R ) and cyclic ketones give lactones. 

The carbonyl group in aldehydes (RCHO) and ketones (RCOR ) is one of the frequently encountered functionalities in the composition of organic compounds. This group has no active hydrogen atoms, excluding the cases of high content of enols for /3-dicarbonyl compounds (/3-diketones, esters of /3-ketocarboxylic acids, etc.) ... 

Spiroannulation The overall conversion of a ketone, RCOR, to a di-a-substituted cyclobutanone. The reaction may be performed by the addition of diphenylsulphoniumcyclopropylide with the ketone RCOR to give the oxaspiropentane that, on treatment with a proton or a Lewis acid, rearranges to give the cyclobutanone. 

Cross-coupling reactions. The Wurtz coupling of an alkyl iodide and an alkyl bromide or two bromides by Sml is catalyzed by a copper salt. Organic chlorides RCl undergo photoinduced dechlorination to afford RH, but under CO the products are ketones RCOR. a,a-Difluorobenzyltrimethylsilane is a useful precursor of the substituted benzyl anion, accessible from cross-coupling of the benzyl chloride and Me SiCl. ... 

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