Replacement of carbonyl-oxygen

There are three main processes for direct replacement of carbonyl-oxygen by hydrogen Clemmensen reduction, catalytic hydrogenation, and reduction by metal hydrides. 

Wheeler, in S. Patai, The Chemistry of the Carbonyl Group, Interscience Publishers, Inc., London-New York-Sydney, 1966. 

The following types of compound can be reduced by the Clemmensen method  

If a carbonyl compound cannot be reduced satisfactorily by the Clemmensen method, the Wolff-Kishner procedure usually gives better results (cf. page 74). 

Clemmensen500 has described the preparation of H-undecane from 2-un-decanone as an example of the reduction of aliphatic ketones to straight-chain hydrocarbons  

---

Sulfur tetrafluoride [7783-60-0] SF, replaces halogen in haloalkanes, haloalkenes, and aryl chlorides, but is only effective (even at elevated temperatures) in the presence of a Lewis acid catalyst. The reagent is most often used in the replacement of carbonyl oxygen with fluorine (15,16). Aldehydes and ketones react readily, particularly if no alpha-hydrogen atoms are present (eg, benzal fluoride [455-31-2] from benzaldehyde), but acids, esters, acid chlorides, and anhydrides are very sluggish. However, these reactions can be catalyzed by Lewis acids (HP, BF, etc). 

Numerous examples of application of DAST for replacement of carbonyl oxygen by fluonne have been reported in the field of carbohydrates [193,194,195] and particularly in the field of s/eroidi [141, 142, 183, 196, 197, 198, 199]... 

Replacement of carbonyl oxygen by nitrogen (imines, hydrazones, osazones etc.)... 

The Wittig reaction consists in the replacement of carbonyl oxygen of aldehydes and ketones by a methylene group with the aid of phosphine-methylenes resulting in the formation of cis or trans olefines. The reaction proceeds through the nucleophilic addition of Wittig reagent (phosphine methylene) across the > C = O bond and formation of an intermediate cyclic. 

The most general and useful application of sulfur tetrafluoride is replacement of carbonyl oxygen and hydroxy groups by fluorine. The reaction has broad scope and is effective with all carbonyl and hydroxy compounds. Alcohols are converted into monofluoro derivatives 1, aldehydes, ketones and quinones into gew-difluoro compounds 2 and 3, and carboxylic acids, acid anhydrides, acid halides and amides into trifluoromethyl compounds 4. 

Esters of carboxylic acids are resistant toward sulfur tetrafluoride up to 300 °C. However, in the presence of an excess of hydrogen fluoride, they react like the acids to give trifluoromethyl compounds [187,235] In contrast, esters of highly fluorinated acids or alcohols react with sulfur tetrafluonde in a hydrogen fluoride solution under mild conditions without cleavage of the ester bond and give products of the replacement of carbonyl oxygen by fluorine a,a-difluoroethers [235, 236, 237, 238] (equations 124 and 125). 

The usual reaction of diethylaminosulfur trifluoride (DAST) with a carbonyl group is the replacement of carbonyl oxygen by two atoms of fluorine, thus generating geminal difluorides. 

The imino group ( = NH), the bivalent ammonia radical, corresponds to bivalent oxygen and compounds result from the replacement of carbonyl oxygen with this imino radical. We have, for example, imino esters and imino acid amides. 

Nucleophilic attack on carbonyl Replacement of carbonyl oxygen Rate and pH chi 2 ... 

Replacement of carbonyl oxygen by selenium under mild conditions CO CSe... 

Sodium hydrogen carbonate/phosphorus pentasulfide Replacement of carbonyl oxygen by sulfur s. 22, 799 suppl. 28... 

Epoxy-5,5-dimethylcyclohexanone allowed to react 2 hrs. at 25 with 1.25 equivalents cyclopropyldiphenylsulfonium fluoroborate and 2 equivalents KOH in dimethyl sulfoxide -> diepoxide (Y 96%) dissolved in pentane and washed with aq. 1 M fluoroboric acid epoxycyclobutanone deriv. (Y ca. 100%) (startg. m. f. 101). - This sequence can be used as part of an annelation process complimentary to the normal Robinson method. F. e., rearrangement also with oxalic acid, s. B. M. Trost and M. J. Bogdanowicz, Am. Soc. 94, Mil (1972) lactone annelation cf. Tetrah. Let. 1973, 923 Am. Soc. 95, 5321 (1973) replacement of carbonyl oxygen by 2 functionalized carbon substituents cf. Am. Soc. 95, 2038, 7862 (1973). 

C-Dialkylation s. Replacement of carbonyl oxygen by 2 carbon substituents... 

A soln. of the startg. m. in ether or methylene chloride added at ca. 5° to a soln. of excess MgBrg prepared from Mg and ethylene bromide in ether, and the product isolated after 15-30 min. a-bromoketone deriv. Y 90%. - Combined with the prepn. of a,/ -oxido- from a-halogeno-sulfones and 0x0 compds. (s. Synth. Meth. 28, 795 suppl. 30), this is a method for the replacement of carbonyl oxygen by both an acyl and a nucleophilic group. F. e., also a-bromoaldehydes, s. F. de Reinach-Hirtzbach and T. Durst, Tetrah. Let. 1976, 3611,... 

---