Reduction of carbonyl functions

Preparation of Alcohols by Reduction of Carbonyl Functional Groups... 

The domain of hydrides and complex hydrides is reduction of carbonyl functions (in aldehydes, ketones, acids and acid derivatives). With the exception of boranes, which add across carbon-carbon multiple bonds and afford, after hydrolysis, hydrogenated products, isolated carbon-carbon double bonds resist reduction with hydrides and complex hydrides. However, a conjugated double bond may be reduced by some hydrides, as well as a triple bond to the double bond (p. 44). Reductions of other functions vary with the hydride reagents. Examples of applications of hydrides are shown in Procedures 14-24 (pp. 207-210). 

In order to transform the spirocyclic enone 445 to ( )-elwesine (439) and ( )-epielwesine (449), it was treated with boron trifluoride and dimethylsulfide to cleave the Al-carbobenzyloxy protecting group, and cyclization of the resulting amino enone spontaneously ensued to produce ( )-dihydrooxocrinine (447). Reduction of carbonyl function of 447 with sodium borohydride afforded ( )-3-epielwesine (449), which was converted to ( )-elwesine (439) by inversion of the hydroxyl function at C-3 via a Mitsunobu protocol using diethyl azodicarboxylate, triphenylphosphine, and formic acid. Attempted reduction of 447 directly to 439 by a Meerwein-Ponndorf-Verley reduction or with bulky hydride reagents gave only mixtures of 449 and 439 that were difficult to separate. 

Review "Reactivity and Stereochemical Factors of the Reduction of Carbonyl Functions with Metallic Borohydride"... 

Hydrosilylation of carbon-oxygen bonds is a mild method for selective reduction of carbonyl functions. Parks and Piers have found that aromatic aldehydes, ketones, and esters are hydrosilylated at room temperature in the presence of 1-4 mol % B(CgF5)3 and 1 equiv. PhsSiFl [154]. On the basis of kinetic experiments the authors suggested that the reduction takes place by an unusual nucleophilic/electrophilic mechanism— the substrate itself serves to nucleophilically activate the Si-H bond, and hydride transfer is facilitated by the borane Lewis aeid (Eq. 99). 

In addition to the aforementioned methods and to those discussed in Chapter 1.14 (this volume), there are several other methods for the reduction of carbonyl functions to the corresponding methylenes. 

The complex [PtCl2(styrene)2] is a catalyst precursor for the hydrosilylation of terminal olefins and acetylenes, the reduction of carbonyl functions (with pyridine or amines as co-catalysts), and for the formation of RaSiOR from RaSiH and alcohols. During the hydrosilylation the complex is reduced to [Pt(styrene)3], which could not be isolated but was characterized by While... 

PEGs are also involved as PTCs in other important reactions such as reaction of mercaptans with polychlorobiphenyl [167], reduction of carbonyl functionality... 

Chiral sulfoxides serve as important building blocks in many areas of organic synthesis [43, 44]. An apphcation is the use of sulfoxides as directing groups in the reduction of carbonyl functional groups [45]. Diastereomeric ketosulfoxides 101 and 105 were prepared by reacting cyclohexanone with (S)-menthyl-p-toluenesulfinate (Scheme 3.23). 

Tosylhydrazones on reaction with alkylithium reagents give olefins in high yield. This new synthesis allowed for exas le the preparation of 16-androstene from androstan-17-one in quantitative yield.Reduction of carbonyl functions to methylene c ui be effected electrochemically or by treatment of the steroid ketones with powdered zinc in acetic anhydride saturated with hydrogen chloride at room temperature." ... 

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