Reduction of alcohols

REDUCTION OF ALCOHOLS, ENOLS, AND PHENOLS I. Reduction of Alcohols 

As a general rule, the reduction of alcohols (R-OH) to hydrocarbons (R-H) cannot be achieved directly. Indeed, the catalytic reduction of other functional groups with hydrogen and metals such as platinum (Pt) or palladium (Pd) at or near room tem- 

the second feature of this process is to hold the osmium in a chiral enviTonment throughout its 

Because osmium(VIII) tetroxide (OSO4) is a Lewis acid, a diastereomeric base pair was sought to insure that either member of an enantiomeric (or diastereomeric) pair of diols can be prepared, that is, 

Although many possible base pairs can be imagined and a number of those have been implemented, the naturally co-occurring epimeric cinchona alkaloids (Chapter 13) quinine and quinidine is one diastereomeric pair that, when converted to their respective dihydrobases by the reduction of the double bond in the side chain, have proved to be a popular, useful, and commercially successful pair. 

The reduction of alcohols to alkanes is not a common reaction because it removes a functional group, leaving fewer options for further reactions. 

We can reduce an alcohol in two steps, by dehydrating it to an alkene, then hydrogenating the alkene. 

Another method for reducing an alcohol involves converting the alcohol to the tosylate ester, then using a hydride reducing agent to displace the tosylate leaving group. This reaction works with most primary and secondary alcohols. 

Predict the products of the following reactions, (a) cyclohexylmethanol -f TsQ/pyridine (c) I-methylcyclohexanol + H2S04,heat 

C2FI4 hydrogenated using hydrogen over a hot nickel catalyst C2H6 To what would propan-2-ol be reduced  

---

Direct Borohydride Reduction of Alcohols to Alkanes with Phosphonium Anhydride Activation N-Proovlbenzene. To a solution of 5.56 g (20 mmol) of triphenylphosphine oxide in 30mL of dry methylene chloride at CfC was added dropwise a solution of 1.57 mL (10 mmol) of triflic anhydride in 30mL of dry methylene chloride. After 15 min when the precipitate appeared, a solution of 1.36g (10 mmol) of 3-phenyl-1-propanol in 10 mL of dry methylene chloride was added and the precipitate vanished in 5 min. An amount of 1.5g (40 mmol) of sodium borohydride was added as a solid all at once and the slurry was stirred at room temperature for... 

Reduction of Alcohols or Ketones. The reaction of alcohols and ketones with chlorine and base to give chloroform is well known (30). 

The two oxidoreductase systems most frequentiy used for preparation of chiral synthons include baker s yeast and horse hver alcohol dehydrogenase (HLAD). The use of baker s yeast has been recendy reviewed in great detail (6,163) and therefore will not be coveted here. The emphasis here is on dehydrogenase-catalyzed oxidation and reduction of alcohols, ketones, and keto acid, oxidations at unsaturated carbon, and Bayer-Vidiger oxidations. 

TABLE 19 Efficiencies and Effectiveness of Water-Air Interfacial Tension Reduction of Alcohol and Alcohol Ether Sulfates... 

Table 16-1. Reduction of alcohols with tri- -butyl stannane via imidazole-Y-thionocarboxylates to the corresponding deoxygenated products.

Intramolecular Friedel-Crafts reactions can sometimes compete with organosil-icon hydride reductions of benzylic-type alcohols to cause formation of undesired products. An example is the attempted reduction of alcohol 26 to the corresponding hydrocarbon. When 26 is treated with triethylsilane in trifluoroacetic acid at room temperature for 15 hours, a mixture of the two fluorene isomers 27 and 28 is obtained in a combined yield of 45%. None of the hydrocarbon structurally related to the substrate alcohol 26 is obtained.171 Whether this problem could be circumvented by running the reduction at a lower temperature or with a different acid remains subject to experimentation. 

Supplemental References for Table 5. Organosilane Reduction of Alcohols... 

Electroreduction of esters (R COOR ) is classified into three types of reaction. The first type of reaction is the reductive cleavage of a bond between oxygen and R. This type of reaction is similar to the cathodic reduction of alcohols (Sect. 7.2) and ethers (Sect. 7.3). That is, activated esters such as allylic and benzylic esters are electrochemically reduced to the corresponding hydrocarbons and acids (Schemes) [1,16,19-21]. 

Hydriodic acid is a reagent of choice for reduction of alcohols [225], some phenols [225], some ketones [227, 228], quinones [222], halogen derivatives [22S, 229], sulfonyl chlorides [230], diazo ketones [231], azides [232], and even some carbon-carbon double bonds [233]. Under very drastic conditions at high temperatmes even polynuclear aromatics and carboxylic acids can be reduced to saturated hydrocarbons but such reactions are hardly ever used nowadays. 

REDUCTION OF ALCOHOLS AND PHENOLS AND THEIR SUBSTITUTION DERIVATIVES... 

Important in maintaining erection and treatment of sterility in men Important in reduction of alcohol toxicity effects and woimd healing... 

---