Affecting the Carbonyl Group

For reactions with lithium aluminum hydride or Grignard reagents converting telluraxanthone to 5-hydroxytelluraxanthenes, see p. 832, 833. 

---

In aryl alkyl ketones, there are two types of C-F bonds to reduce. Fluorine atoms in the a-positions are usually more easily replaced than those on the aromatic ring. It is also possible to reduce a-C-F bonds selectively without affecting the carbonyl group. 

The only known method enabling a selective replacement of a-fluorine substituents in aliphatic polyfluorinated esters without affecting the carbonyl group is pholoinduced reduction (e. g., 1 - 2) the reaction yield is dependent on the solvent (hydrogen donor) used, e. g. propan-2-ol > tetrahydrofuran > 1,3-dioxolane.106 The reactivity of fluorinated esters is also dependent on the group attached to the /(-carbon, e. g. 3 > 4 > 5.106... 

How -elimination reactions and subsequent processes under alkaline conditions affect the carbonyl groups and the Mw of an oxidized cotton linters is shown in Fig. 2. The initial concentration of carbonyls is 30 pmol/g, introduced by hypochlorite treatment at pH 7. The sample was treated with a buffer solution of pH 11 at 40 °C. The Mw suffers a steep decrease within the first 5 hours, the drop in carbonyls proceeds at a significantly lower rate. While the changes in Mw level off after approx. 20 hours of treatment, the carbonyl groups are slightly decreasing further (unpublished results). 

Dialkyl cadmium was employed to convert ort/io-substituted phenyl tellurium halides to unsymmetrical diorgano tellurium products. These conversions were accomplished without affecting the carbonyl groups present in the molecules. 

Other reactions afFecting the carbonyl group in alkyl aryl tellurium compounds are summarized below ... 

The alkylthio group in an aromatic ketone may be removed with Raney Ni without affecting the carbonyl group. Thus, treatment of desyl thioethers (a-alkylthiodesoxy-benzoins) with Raney Ni, which had been deactivated by refluxing in acetone,149 gave desoxybenzoins in yields of 55-90% (eq. 13.73).150... 

Unconjugated unsaturated aldehydes and ketones can be reduced without affecting the carbonyl group, particularly with a Pd catalyst Ni and Pt have been used, but the reduction must be terminated after the addition of 1 equiv. of hydrogen. The nitrile group also can survive the reduction of carbon-carbon unsaturation in the same molecule. 

Hydrogenation will remove even a conjugated double bond without affecting the carbonyl group (Chapter 14) or an aromatic ring. 

Although chromone-3-carboxaldehyde is readily prepared, the 2-isomer is much less readily available. Selective reduction of methyl chromone-2-carbox-ylate with NaBH4 and MeOH has given the 2-hydroxymethyl compound, apparently without affecting the carbonyl group of the pyrone oxidation with... 

With organolithium compounds, their substitution reactions proceed without affecting the carbonyl groups as shown in eq. (3.14), and in this regard they are different from Grignard reactions [34]. 

---