Carbonyl group trichloromethyl groups

The carbonyl carbon of perfluoro acyl halides and carboxylic acids can be converted to a trichloromethyl group [67] (equation 54)... 

Attempts to produce chiral cyanhydrins under phase-transfer catalytic conditions (3.3.9) using ephedrinium or cinchoninium catalysts has been singularly unsuccessful [21,22]. Optical purities varying from 0 to 60% have been recorded [22], but verification of the reproducibility of the higher values is needed. Similarly, nucleophilic attack on a carbonyl group by the trichloromethyl anion under phase-transfer catalytic conditions (see Section 7.4) in the presence of benzylquininium chloride produces a chiral product, but only with an enantiomeric excess of 5.7% [23]. The veracity of this observation has also been questioned [24],... 

The instability of the /3-oxo acids is a result of the electron-withdrawing carbonyl group which acts as an electron sink for the pair of electrons withdrawn from the carbon-carbon bond undergoing cleavage. Other electron-withdrawing groups such as nitro and trichloromethyl groups act in a similar manner.353... 

These stability effects are apparent in the equilibrium constants for hydration of ketones and aldehydes. Ketones have values of Keq of about 10-4 to 10-2. For most aldehydes, the equilibrium constant for hydration is close to 1. Formaldehyde, with no alkyl groups bonded to the carbonyl carbon, has a hydration equilibrium constant of about 40. Strongly electron-withdrawing substituents on the alkyl group of a ketone or aldehyde also destabilize the carbonyl group and favor the hydrate. Chloral (trichloroacetaldehyde) has an electron-withdrawing trichloromethyl group that favors the hydrate. Chloral forms a stable, crystalline hydrate that became famous in the movies as knockout drops or a Mickey Finn. 

Trichhromethylation of anhydrides. When the salt is decomposed in 1,2-di-mcthoxyethane in the presence of an olefinic anhydride, reaction occurs exclusively at a carbonyl group of the anhydride, apparently by the trichloromethyl anion precursor of the carbene, to give the trichloromethyl addition product. Yields are erratic, ranging from 80 to 8%. 

Since the cyclopropanation is rather slow, it is postulated that the formation of dichlorooxirane goes via the addition of the trichloromethyl anion to the carbonyl group, then the cyclization of the adduct the intermediate oxirane 11 was isolated after 30-40% conversion of ketone. 

Trichloromethyl and carbonyl groups react at or below room temperature when the compound is stirred with methylamine, and the former substituent is lost. 

Under the influence of potassium hydroxide, chloroform can also be added to carbonyl groups this affords trichloromethyl alcohols, e.g. ... 

From a-trichloromethyl carbinols with the hydroxy group at a tertiary carbon, either dichlorovinyl compounds or, after rearrangement, carbonyl compounds are formed predominantly. The pathway of the reaction can be influenced by the choice of the reaction conditions. As the reduction potentials of some of the substrates are... 

Bis(trichloromethyl) carbonate ( triphosgene ) is described as a more convenient reagent than phosgene and other reagents as a source of a CO group. This is well exemplified in the synthesis of a 2-benzoxazolone from a 2-aminophenol at ambient tem(>erature (3617]. Carbonyl sulphide is another reagent which is worth considering in this synthesis (3096]. An aminophenol may be cyclized... 

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