Preparing Alcohols from Carbonyl Compounds

We ve already seen several methods of alcohol synthesis  

Alcohols can be prepared by hydration of alkenes. Because the direct hydration of alkenes with aqueous acid is generally a poor reaction in the laboratory, two indirect methods are commonly used. Hydroboration/ oxidation yields the product of syn, non-Markovnikov hydration, whereas oxymercuration/reduction yields the product of Markovnikov hydration (Section 8.4). 

2-Diols can be prepared either by direct hydroxylation of an alkene with OSO4 followed by reduction with NaHSOa or by acid-catalyzed hydrolysis of an epoxide (Section 8.7). The OSO4 reaction occurs with syn stereochemistry to give a cis diol, and epoxide opening occurs with anti stereochemistry to give a trans diol. 

CHAPTER 13 ALCOHOLS, PHENOLS, AND THIOLS ETHERS AND SULFIDES 

REDUCTION OF ALDEHYDES AND KETONES Aldehydes are reduced to give primary alcohols, and ketones are reduced to give secondary alcohols  

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Allylsilane and Propargylsilane Synthesis. (lodomethyl)-trimethylsilane has been used to prepare aflylsUanes, which are t)q)icafly utilized in Lewis acid or fluoride ion-promoted reactions with carbonyl compounds to provide homoallylic alcohols. Treatment of Mc3SiCH2l with methyltriphenylphosphonium bromide and base produces an intermediate phosphonium salt which can be further utilized to prepare allylsilanes from carbonyl compounds. This procedure has been modified so that this series of transformations can be done as a one-pot procedure (eq 1). ... 

Alcohols can be prepared from carbonyl compounds by reduction of aide hydes and ketones See Table 15 3... 

The most generally useful method for preparing alkyl halides is to make them from alcohols, which themselves can be obtained from carbonyl compounds, as we ll see in Sections 17.4 and 17.5. Because of the importance of the process, many different methods have been developed to transform alcohols into alkyl halides. The simplest method is to treat the alcohol with HC1, HBr, or HI. For rea-... 

Direct electrochemical oxidation is not a convenient way for a preparative production of carbonyl compounds from alcohols due to the unselectivity caused by the high oxidation potentials of alcohols. Thus, there have been only a few compounds (some aliphatic alcohols, glycols, and related alcohols) that have been oxidized by the direct method, while the indirect method has often been used to oxidize selectively a variety of alcohols, since it does not... 

Alcohols may be prepared (1) by hydration of alkenes (1) in presence of an acid and (11) by hydroboratlon-oxidatlon reaction (2) from carbonyl compounds by (1) catalytic reduction and (11) the action of Grignard reagents. Phenols may be prepared by (1) substitution of (1) halogen atom In haloarenes and (11) sulphonic acid group In aiyl sulphonic acids, by -OH group (2) by hydrolysis of diazonium salts and (3) industrially from cumene. 

One can also acetalize carbonyl compounds completely without using the alcohol in excess. This is the case when one prepares dimethyl or diethyl acetals from carbonyl compounds with the help of the ortho formic acid esters trimethyl ortho formate HC(OCH3)3 or triethyl ortho formate HC(OC2H5)3, respectively. In order to understand these reactions, one must first clearly understand the mechanism for the hydrolysis of an orthoester to a normal ester (Figure 9.13). ft corresponds nearly step by step to the mechanism of hydrolysis of 0,0-acetals, which was detailed in Figure 9.12. The fact that the individual steps are analogous becomes very clear (see Figure 9.13) when one takes successive looks at... 

Oxazolidines are commonly prepared from /3-amino alcohols and carbonyl compounds (equation 173). The condensation is conveniently conducted in boiling benzene with continuous removal of water. Treatment of 2-aminoethanol with formaldehyde yields the parent compound (67BSF571). An interesting reaction is the formation of the enantiomerically pure oxazolidine (307) from (-)-ephedrine and the alkynic sulfone PhS02C=CMe (79JCS(P1)1430). 

Reduction of the carbonyl function in acetophenones using sodium in ethanol also produces an alcohol. More complex aromatic alcohols may be prepared from carbonyl compounds by reaction with Grignard reagents followed by hydrolysis (see Chapter 10). 

Acetals and ketals are readily prepared from carbonyl compounds and orthoformic esters in alcohol solution in the presence of a catalyst such as concentrated sulfuric acid, anhydrous hydrogen chloride, or ammonium chloride (60-95%)/ The reaction mixture must be neutralized before processing since the acetals are very sensitive to an acid hydrolysis. The methyl and ethyl esters of orthosilicic acid have been substituted for the ortfioformic esters with good results (70-90%) however, steps must be taken to remove compounds of silicon. ... 

N-Bromobenzopbenoneimine, (C5Hs)2C = NBr (mp 38.5 °C) [747], which is prepared from benzophenoneimine, bromine, and alkalies, is used for the conversion of alcohols into carbonyl compounds [748]. 

MTO has also been claimed to be the first transition metal complex to catalyze the direct, solvent-independent formation of ethers from alcohols [30]. Aromatic alcohols give better yields than aliphatic ones and reactions between different alcohols have been used to prepare asymmetric ethers. Also catalyzed by 1 is the dehydration of alcohols to form olefins at room temperature. When primary or secondary amines, respectively, are used as the limiting reagents, direct amination of alcohols gives the expected secondary or tertiary amines in yields of ca. 95 %. Disproportionation of alcohols to carbonyl compounds and alkanes is also observed for aromatic alcohols in the presence of MTO as catalyst. 

Allylic oxidation. This novel oxidizing agent is prepared from C6p6 and NaSeH followed by exposing the product to O2, O3, and H2O in sequence. It converts alkenes to enones, besides oxidizing alcohols to carbonyl compounds. 

Lithiated 1,3-dithianes react readily with epoxides to give thio-acetals of 13-hydroxy aldehydes or ketones. Addition of carbonyl electrophiles to 2-lithio-1,3-dithiane is efficient and provides a method for preparing a-hydroxy carbonyl compounds. For example, the ketone 120 can be converted into the hydroxy aldehyde 122 via the alcohol 121 (1.108). The dithiane approaches the ketone from the less-hindered convex face of the fused ring system. 

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